The problem is not with size, but rather with the fact that there can't be more than 10 control sprites on the screen at the same time and the 10 are full. The palette is also full, so it couldn't be solved with that either. :(
Guess what, I don't even have a Gameboy, or even a Color, just a 3DS. :)
Did you know that if you press START continuously and start the game like that, it will run in the original resolution?