Why not ask if you can send it back and get a 2x2x4? I assume you bought from LLL, and the 2x2x3 is more expensive than the 2x2x4, so i'd assume they would send a new one if you payed for shipping?
I would not put a small/baby chameleon in a 2x2x4, or at least not with the more common larger species like panthers and veileds.