Thanks for playing the game! Two things come to my head:
- Just in case, have you tried holding the jump button? The longer you hold, the higher you jump.
- Some people on slower machines or browsers get stuck because you jump a bit less high when the framerate is low :( Since this was an entry for a game jam, I didn't have the time to code a proper fix for this bug. I'm really sorry if this is the case. I'd suggest trying with a different browser, such as Firefox Quantum, or a different computer and see if it helps.