This is a nice start to what could be a decent platformer.
I also make my own assets during the jam so I know the it increases the challenge because you need to allow time to create the art, sounds, music and the game, all within the timeframe.
As others have said, there needs to be goal to give you a target to aim for, and then you can probably add more levels. With the concept being close to ships in bottles, you could also add items you need to pick up that look like little sailing ships? Maybe that's what needs collecting to progress past the cork at the end (when you implement it).
Thanks for the game.