First of all, I just want to say, congratulations on finishing your first game! For someone who's new to gamejams and probably even game development as a whole, you actually made a pretty enjoyable game. Some of my favorite things from it were the particles when bullets collide and/or something dies, the Celeste-like dash aswell as the cool boss fight at the end.
A few quick suggestions of mine are, when the player takes damage and flashes, make the color the player flashes a bit darker or lighter because, when you get hurt, your character starts to blend in with the background and when you deal damage to an enemy, have the enemy flash red just like the player to show that you are actually doing damage because, currently its feels as if enemies are taking no damage at all from my projectiles.
This was a short but fun game to play that I would totally recommend other people to try and I hope to see more games from this creator in the future.
This is what I mean by the character blends in