Overall not an awful game however there are some things that could definitely be improved. I understand this is your first game jam but critique is still useful.
Some of the physics feel a little off. Gdevelops platformer behavior is pretty good but I would tinker with it more to make things a little tighter. Generally increasing the fall speed helps things feel better.
Also there aren't any instructions on how to play. At the bare minimum there should be some indication that you can double jump because I was legitimately confused for a little bit on how to make the first big jump.
Also with Gdevelop pixel smoothing is enabled by default so when making pixel art games make sure to turn on pixel perfect when making the project or go to the resources tab to disable smoothing on such sprites.
Hope this helps :)