One thing to keep in mind is that having a new key cut from the code looked up at the dealer means you're using a new key on a worn lock cylinder & it may not work if the cylinder is really worn. We would have that problem occasionally at the Nissan dealership I used to work at - the keys would get locked in a car or lost so we'd cut a new key from the key code but it wouldn't turn in the lock cylinder.
Getting a locksmith to cut you a key from your fuel door lock cylinder is a better bet.

95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes