For a first game, you should be proud! Most people who want to make games never even finish a product, so to not only start making, but also to finish a game is an accomplishment in and of itself. Especially in 48 hours. So congratulations on that.
This is an interesting concept. I like how it makes you pick you shots more conservatively than you otherwise would in a game like this. The shape of the level also leads to more interesting bounces of your own projectiles. I wish there was more feedback in the game, though. More sounds, more colors, etc. Everything was a bit small, so it was easy for me to lose track of my own bullets, which was a problem when they were trying to kill me. With a couple more enemy types, you could have a nice little game here.