Let's start with the things you could improve on.
First - audio, but that's understandable in a game jam.
Gameplay - it became boring too fast, I didn't see a reason to play after buying the first upgrade, I think I experienced the full game, but I am not sure, you can tell me. If so there was nothing to do after that.
To end this on a nice note: The graphics were really good for a 3 day gamejam.
Still, you can be proud you actually finished and delivered a game.
Keep it up!