I really like this, it's especially good considering it's your first jam. I liked the mechanic of bouncing bullets rather than really wild, crazy patterns.
One thing to consider is the difficulty curve - even on hard mode I found myself pretty bored for the first 20-30 seconds. Perhaps starting by having 5 or 6 balls shoot out right at the beginning? The most fun was between about 45 seconds to 70 seconds, so if you can figure out a way to get the player into that window faster that would be great!
Nice work on this!