Things I liked:
The level design was great! With just 3 levels, you seem to have made the most of the movement mechanics. The difficulty of each level relative to each other was also great. I like how each level increased in difficulty by a substantial amount. The art/animations and music also enhanced the experience.
Potential improvements:
You give the player leeway when pressing jump before actually touching the ground, so I think you should give leeway when the player presses jump a fraction of a second after leaving a jumpable platform as well (like coyote time in Celeste). It would also feel better if the platforms didn't feel so... slippery. I think those changes would make the movement a lot more fun. I think the placements of the heart fragments could be improved as well, because currently it pretty much takes the same amount of skill to get ending 2 and 3.
Overall, great game, especially for a game jam. I would love to see more levels!