First of all, congrats on your very first jam game! I hope you felt that the 4 days of arduous work (especially since you worked on almost all of the assets) was worth it!
The game as a premise was nice and interesting, and it caught my attention when I read the description. For a simple jam game, I think that overall it is a good game. But unfortunately it sort of lost my attention after the second stage. If it had something to show more than just extra obstacles and enemies, I wonder how much the game would play out. I'm not sure if it's what you're going for, but maybe upgrades to your character, such as longer lifespan, or multiple projectiles, etc.
I want to reiterate that the fact that you made all of the assets, because that is testament to your dedication! Congrats again, hopefully post jam you can make this game super cool!