Honestly pretty darn good. especially in its presentation (visuals/audio).
Just like another comment said, make the game ramp up faster (like give use the orange power-up in stage 3). That would enhance it for a game-jam. Projectiles are indeed quite small, but If I spam a little bit then I'll eventually hit with one of them.
Personally, I think it would be good if you could charge a shot, increasing its size.
And perhaps also a ray indicating the line of your shot, which slowly fades out the farther it goes (like make it almost invisible 1/2 the screen width or something). Just spitballing some concepts I got during play.
You should really think about updating the page with a few screenshots and/or a new thumbnail.
I think it would be a shame if people gloss over what you've made due to lack of eye-catchiness.
I tend to hover over games in the submissions after which I'm presented with the screenshots they have put on their page. those screenshots typically win me over to check them out.
Nicely made, hope more people notice this one too.