Good stuff! We all start somewhere, and getting a project of any size completed and successfully released is an awesome first step - especially within the restrictions of a Game Jam! Hope you keep working on more stuff in the future.
As a next step, music and sound effects can really help bring a game to life, and it's pretty simple to implement in Godot with a little practice. To get a song playing uninterrupted throughout the entire project, import the song into your project with loop toggled, add the song to a AudioPlayer node, make it autoplay, and make the scene an autoload. There's some good guides on Youtube to follow along to.
Freemusicarchive and Pixabay are great places to find some CC0 tracks.
SFX are a little more complex, but once you've got the hang of the audioplayer it just becomes a matter of triggers. Chiptone which you can find on Itch is a fun way to generate your own SFX for retro games.