The idea is cool and although the mechanic was simple, I enjoyed it.
There was some problems with the controls and player character that were frustrating for me. Climbing on your own projectiles to get past some obstacles is not very intuitive out of the blue I think. They disappear too quickly also. Maybe instead of deleting them over time, you could have a limit of two projectiles so that the player has more time to climb. There is also a problem with the character blocking its own projectiles if you shoot in certain directions.
Apart from the mechanics, I would just add a two frame animation for the character so that it feels a bit more dynamic.
Overall, congrats on submitting your first game to GWJ! I hope this feedback can be useful for you :)