Congrats on submitting your first jam game. You should feel proud of yourself.
I really like the idea behind this game, but I do have some questions regarding gameplay. How much more is there after the locked door on the right, after the spaced jumps? I explored everywhere that I could except I couldn't get past that door. I assume I can after fighting the first boss, but there are other issues that prevent me from getting back to that door such as the wall enemies rapidly firing projectiles. Also, the player moves reaaally slow. Was there a point behind that? Like later on in the game, does the player get speed powerups? The game mentions a dash, but it either doesn't work, or its a powerup I never reached.
EDIT:
Just to double check myself, I played the game again with the same issues, but I noticed that you get the ability to block projectiles if you press down, which helps navigate the rapid fire wall enemies, but the route with the spikes still prevented me from progressing. Also, as a general rule, if you acquire a powerup, you want to make sure your player knows they did. I knew I beat a boss and I knew I picked something up, but my hearts refilled and I just made the assumption that it was just a full health replenish.
Viewport sizing was a little weird to me as well. Fullscreen felt too zoomed in, but outside of fullscreen mode, your UI moves to an odd position.
Music and art meshed well together, which can be hard to get right sometimes, so good job there.
I know this sounds like a lot of nit picky stuff, but I like to bring up these kinds of issues, questions, and help you generate insight into your own progress as a developer. People did this for me during my first mvm and I improved vastly. I even come back to previous feedback to see if I'm repeating something that people didn't like in general.
Overall, its not a bad first jam game. If you can provide a little more information, I'll try to come back and progress further than last time. Other than that, congrats on submitting.! You have a lot of room to grow and you should be excited by that. Keep entering this jam, there's quite a few of us who participate regularly and its great to see how we all grow!