Hey. Nice job for your first game jam entry. I've got a few suggestions that might help. Things are a bit too tiny as they are. Adding a full screen button could help (you can choose this in "edit game" page of itch.io for your game). Making the sprites a bit larger also helps. Not all of us have very young eyes you know! :)
Your character sprite is a bit blurry. You can fix this (if you want a sharper look) by selecting the image file in Godot, going to the import tab, deselecting "filter" and clicking re-import.
About the "source" field which you wrote you don't know what it means. It's simply asking you if you want to share the source code of the game. If you want, you can put a github link in there. It's entirely optional of course.