You got a great solid idea. I like the concept of growing outside the arena after each fight, btu still being able to see the small arena. It gives a great sense of accomplishment and how far you have come. The actual gunplay could use a little more work if you had the time, some sound effects and little particle effects would really make it pop and feel satisfying. But these little polishes aside amazing work getting a game done in time! And with such a cool core concept! :D

The idea is okay, but without sound effects and perhaps a bit animations, It's difficult to know what is happening.   

lol, what a cute little game.
The player size doesn't really tie into the gameplay much. Maybe if there was a way to grow during the fight and get an advantage instead of between fights it would become more interesting!