I like this game, it's nice and simple and has a super cool implementation of the theme. My mind somehow went straight to 'the edge of flat earth' after I saw the theme too, but I couldn't think of a way to implement it. But you did it well!
The movement does seem a little finicky/jittery for some reason though. It's almost like the ship has inertia sometimes but can immediately stop at other times? I can't pinpoint the exact reason, but maybe you could work on that if you want to extend this game in the future.
Overall, this was a fun game. I was able to score 26! Thanks for making it :)