Well, it is 'released' for sake of the game jam. I presume that the rules of the jam mean I can't continue to work on it whilst people are voting on it? I don't know how these things work really - it's my first jam!
Anyway, I'm going to leave this game as it is, and consider it a fully functioning prototype. If I do want to take it further and build on it, I'm going to make a new version from scratch with the game engine that I normally use and feel more confident with (Godot).
Thanks for your feedback - it gives me something to think about.