As others have stated, the audio is a bit loud. The AudioStreamPlayer2D has the DB setting, if the audio file you import is very loud you can set that to a max of -35 DB I think to bring that volume down. Otherwise download Audacity, great audio program to manipulate tracks, and you can adjust the track volume, then export to Godot.
Great concept and good entry point for a puzzler/platformer style game. Don't worry too much about ART at this stage, I start all my builds off with different sizes of the godot icon. It works and allows me to focus on mechanics. Well done, keep at it!