Here's some feedback on your game:
1. The theme
The concept is really interesting, i'm glad to see something unique after all the "there's something in the middle and you have to shoot things around it to protect it" games XD. (Don't get me wrong, they are good, but there are just so many of them!)
2. The gameplay
I think the game really introduces its mechanics well, but (for me at least) it was way too difficult and thus a bit frustrating.
3. The Graphics
The graphics look simple, but really nice, really shows how much you can do with a nice font and color scheme (many people can draw very well but just don't do these points right).
4. The sound
I don't think there are any sound effects, are there? Maybe add some! Also, i think i know that music from somewhere, did you make it yourself or what is it called?
I hope my feedback helped you, overall this is a solid submission, i think it will be ranked pretty high, good luck in your futre jams! :)