Thank you for your feedback! As you and others said there are some aspects of the game that aren't really polished, but I'm planning on updating and fixing the game with all the feedback I recieve after the jam ends.
About the boss, I know it's not clear what you have to do, but there is a win condition, not getting shot at any moment (also not shooting yourself due to a bug), and shooting the boss, even if you damage yourself as you can see that the healthbar goes lower. At the end (SPOILER) you end up killing him, but you also die trying.