I will tell you a secret, guys. Actually, Alan works at Lamborghini
Below is a cross-section test I did today on the 3d model, just to show how the separate pieces correspond together and what's the clearance around the pivot point of the fuel door.
http://imageshack.us/a/img191/1778/f8z0.png http://imageshack.us/a/img823/7199/uoit.png http://imageshack.us/a/img593/9314/no5u.png By the way, that extra 3rd piece (the tab shown in red) is meant to be made from steel, while a super magnet is bonded at the back of the fuel door. However, I'm not sure if it's safe to place magnets near the fuel opening. But this is certainly the most minimalistic way to do the locking mechanism.
http://imageshack.us/a/img407/1212/0yg4.png An alternative way to keep the fuel door closed is to use a spring, but it will look a bit ugly when opened. A synthetic plastic wire (not metal one to prevent damage on the part) could be used where the white line is, while the actual spring is hidden behind so that there is no way to see it from outside. But I think that the magnet option is better in case that it's not dangerous for causing fire.
Another way is to make the red tab part of the fuel door, and make a hole in the tab so that a remore controleed pin exiting from the main cylindrical body (in the very same way that the yellow screw goes there) will go through the red tab to secure the fuel door.