Great submission, congrats on your first jam!
If you wanna work on a post jam version, I think you could add more sprites for the character (for falling, jumping, jumping at high speed, dead, etc). Also, the distance to the Moon on screen could be great to have a sense of progression. Finally, I'm not sure but maybe the background could get improved by using some layers and parallax.
Once again: good job! Keep motivated and working!