You're not the only one that found aiming difficult - for you and anyone else who found the keyboard controls a little difficult, I've updated the build so that you now shoot the direction you're facing if you're not aiming with the arrow keys/right stick! Hopefully that makes things a little easier, so give it another shot!
As to infinite ammo, we can't really do that because the entire point of the game is managing your ammo. If we'd done a little more playtesting and had time though, I think I would've added in a weak melee attack, so if you run out of ammo you still have a chance to defend yourself and grow more ammo.
Thanks for the feedback, and I hope you have a chance to play it again with controls that work better for you!