That's pretty cool. Got to 46 after a couple of tries. I like how you went with a chill vibe with the relaxing music. I like the concept of making the enemies grow until they explode. I found it hard to know where my cursor was, at least at first, maybe you could make it a bit more visible. Also, if it helps, I skipped the help and went straight into playing then lost a few times trying to figure out how to play.
Flatland homing asteroids :-)
You should add an animated GIF demo to the README. Hiding the demo behind a link does no good.