I need more ammo! haha its really difficult to get past the first level without more then 5 shots and not being able to jump properly. That might be a bit much for level one.
you should really consider easy level design building up into stuff that is harder and harder with the type of mechanics you are running. That or have 1 bullet always kill whatever its hitting. because if 3 rats spawn, its impossible to kill all three then jump without dying.