Decent start, but a few glaring flaws
I recognize that this game was made with very little time. The basic stuff is there, and it is definitely playable. However, given what the player can do, there's a few errors that one can do "wrong" that aren't obvious.
A complaint that would immediately rise up is the confines of the camera view, in that you can't see much of the playing area where the asteroids come from. This will cause the player to move around to detect any incoming asteroids.
The freedom of movement that the player is given is a deception and detrimental however: asteroids only spawn at the top of the player's point of view. Most players jumping in the game for the first time won't realize this (me included).
What will end up happening is that asteroids will swarm the planet from all sides. A pro player will just shoot the small asteroids once, the large ones twice, then move on. This does not work, because the bullets disappear once they go off screen, and the asteroids remain. This causes an overwhelming amount of asteroids to close in, and the player can't do much about it.
Currently, the correct way to score high and live long in this game is to only move for ammo drops if they're on your side of the planet, but otherwise try to restrict your range of movement as much as possible during each wave. Shoot all asteroids down obviously.
One last thing: the ammo drops behave strangely, as if the expiration timer doesn't reset when a new drop appears.
Having said all that, you seem to have potential. Take more time to develop your projects, and get a beta tester so he/she can catch things that you as the dev may not catch, so terrible design issues like the ones I described don't happen again.