If you have only two different textures so far, the [fltsim.0] entry pertains to the original, the first texture.
Now you've named your additional livery: texture.3.
Even though the name is <3> the following entry in your aircraft.cfg has to be [fltsim.1] NOT [fltsim.3].
If you add another livery/texture the subsequent entry has to start with [fltsim.2] ...and so on.
This can get confusing that's why it's much better to give your individual textures names instead of numbers.
As an example the original texture could be named AA, the next one Virgin Atlantic, the next one SIA and so on.
Here's an example of my MD-11 .cfg with 21 different textures:
[fltsim.0]
title=iFDG MD11 Swiss
sim=MD-11
model=PW_PAX
panel=
sound=
texture=Swiss
atc_id=HB-IWC
atc_airline=Swiss
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Swiss
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.1]
title=iFDG MD11 Aer Lingus
sim=MD-11
model=PW_PAX
panel=
sound=
texture=EI
atc_id=N272WA
atc_airline=SHAMROCK
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Aer Lingus
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.2]
title=iFDG MD11 Alitalia
sim=MD-11
model=PW_PAX
panel=
sound=
texture=AZ
atc_id=HB-IWC
atc_airline=Alitalia
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Alitalia
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.3]
title=iFDG MD11 McDonnell Douglas City Bird
sim=MD-11
model=PW_PAX
panel=
sound=
texture=CTB
atc_id=OO-CTB
atc_airline=Dream Flight
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=City Bird
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.4]
title=iFDG MD11 McDonnell Douglas Federal Express(FedEx)
sim=MD-11
model=GE_F_B
panel=
sound=
texture=fedex
atc_id=N601FE
atc_airline=Fedex
atc_flight_number=FX011
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11F
ui_variation=Federal Express (FedEX)
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.5]
title=iFDG MD11 McDonnell Douglas Japan Air Lines 1.5
sim=MD-11
model=PW_PAX
panel=
sound=
texture=JAL
atc_id=JA8584
atc_airline=Japan Air Lines
atc_flight_number=JAL589
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Japan Air Lines
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.6]
title=iFDG MD11 Japan Airlines NC
sim=MD-11
model=PW_PAX
panel=
sound=
texture=JAL NC
atc_id=JA8582
atc_airline=JAPAN AIR
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Japan Airlines NC
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.7]
title=iFDG MD11 McDonnell Douglas KLM Royal Dutch Airlines
sim=MD-11
model=MD11PGE
panel=
sound=
texture=KLM
atc_id=PH-KCD
atc_airline=KLM
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=KLM Royal Dutch Airlines
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.8]
title=iFDG MD11 McDonnell Douglas Korean Air MD-11 PAX
sim=MD-11
model=PW_PAX
panel=
sound=
texture=KAL
atc_id=HL7374
atc_airline=Korean Air
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Korean Air
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.9]
title=iFDG MD11 Saudia VIP
sim=MD-11
model=GE_PAX_A
panel=
sound=
texture=SA_VIP
atc_id=HZ-HM7
atc_airline=Saudi
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Saudi Arabian Airlines
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.10]
title=iFDG MD11 Swissair
sim=MD-11
model=PW_PAX
panel=
sound=
texture=Swissair
atc_id=HB-IWA
atc_airline=SWISSAIR
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Swissair
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.11]
title=iFDG MD11 McDonnell Douglas Thai Airways International
sim=MD-11
model=GE_PAX_B
panel=
sound=
texture=thai
atc_id=HS-TMD
atc_airline=Thai
atc_flight_number=TB118
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Thai Airways International
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.12]
title=iFDG MD11 Varig
sim=MD-11
model=GE_PAX_B
panel=
sound=
texture=Varig
atc_id=PP-VQJ
atc_airline=VARIG
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Varig
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.13]
title=iFDG MD11 Lufthansa Cargo
sim=MD-11
model=GE_F_B
panel=
sound=
texture=LH_Cargo
atc_id=D-ALCG
atc_airline=LUFTHANSA
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11F
ui_variation=Lufthansa Cargo AG
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.14]
title=iFDG MD11 United Parcel Service
sim=MD-11
model=GE_F_A
panel=
sound=
texture=UPS
atc_id=N252UP
atc_airline=UPS
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11F
ui_variation=UPS
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.15]
title=McDonnell Douglas MD-11 JAL Japan Airlines #JA8587
sim=MD-11
model=GE_PAX_A
panel=
sound=
texture=jal_8587
kb_checklists=
kb_reference=MD11_ref
atc_id=JA8587
atc_airline=Japan Air
atc_flight_number=732
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=JAL Japan Airlines #JA8587
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.16]
title=McDonnell Douglas MD-11 Saudi Arabian "Royal Flight"
sim=MD-11
model=GE_PAX_A
panel=
sound=
texture=saudi
kb_checklists=
kb_reference=MD11_ref
atc_id=HZ-AFA1
atc_airline=Saudia
atc_flight_number=11045
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Saudi Arabian "Royal Flight"
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.17]
title=iFDG MD11 Thai Airways
sim=MD-11
model=GE_PAX
panel=
sound=
texture=HS
atc_id=HS-TMD
atc_airline=THAI
atc_flight_number=381
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Thai Airways NC
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.18]
title=iFDG MD11 McDonnell Douglas Saudi Arabian cargo
sim=MD-11
model=GE_F_A
panel=
sound=
texture=sac
atc_id=HZ-ANB
atc_airline=Saudi
atc_flight_number=184
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11F
ui_variation=Saudi Arabian Cargo
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.19]
title=iFDG MD11 Fedex
sim=MD-11
model=GE_F_B
panel=
sound=
texture=fedexpro
atc_id=N601FE
atc_airline=Federal Express
atc_flight_number=114
atc_heavy=1
ui_manufacturer=McDonnell Douglas
ui_type=MD-11F
ui_variation=Federal Express (Pro)
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
[fltsim.20]
title=iFDG MD11 McDonnell Douglas GIA EI-CDK
sim=MD-11
model=MD11PGE
panel=
sound=
texture=cdk
atc_id=EI-CDK
atc_airline=GARUDA
atc_flight_number=GA8114
atc_heavy=1
atc_parking_types=GATE, RAMP, CARGO
atc_parking_code=GIA
ui_manufacturer=McDonnell Douglas
ui_type=MD-11
ui_variation=Garuda Indonesia EI-CDK
prop_anim_ratio=1.76
visual_damage=1
description=McDonnell Douglas MD11 FDE by Albaro Villegas\n
You see that each texture has a name rather than a number.
NOTE: I said 21 different textures even though the last entry is [fltsim.20] -- the first entry [fltsim.0] counts as well so that brings as to a total of 21.