A fun and efficient little platformer, I appreciate the time you took polishing this. I love the double jump animation, that's a nice touch.
In terms of mechanics, it's a little bit dry for a platformer. Without any player acceleration, the game feels a bit too "fake", like there isn't any weight on the character. I also don't think there is any coyote time, as I lost my double jump quite a few times while jumping from a platform.
I understand these mechanics aren't easy to implement in a jam, esp since it's your first. I think you focused on the most important part : making a full fledged, polished game. Congrats !