Had great fun playing this :) I eventually made it to 2-1 (which I believe is one of the endings?)
The game is very well made, although there were a few minor things that were a bit annoying and are likely quite easy to fix:
Dying is quite punishing since you have to wait a bit before you can start your next attempt, maybe it would be a good chance to respond to the player at the checkpoint instead of bringing them back to the level selection screen.It was also a bit annoying that I was able to move the player then the intro to the level was still playing, you might want to disable input during this.
* UPDATE: Read in the comments that you already fixed this for post-jam! :)
Very impressive stuff for a 1 week game jam! Keep up the good work :)