Thanks for playing our game!
I wasn't as involved with the coding, so I can't say much about the fullscreen issues, but it might work better in a different browser.
You bring up an interesting point with the hearts. I believe the idea was originally from earlier in development, before variable scoring had been implemented, to prevent the player from simply spamming cuts for a perfect score. We might have revisited the concept of the fail-state if we'd had the time, but at the very least we didn't think the hearts detracted from the game enough to justify removing in the end, considering what little time we had.
Though, I think they still somewhat serve their purpose, especially in the context of a jam where reviewers might not be as familiar with rhythm games. If there were no hearts, someone who is not concerned with score might simply spam inputs and hit every cut, thereby "winning" the game in their mind and moving on without really experiencing what the game is about.
(Also, just to flex, my highscore is over 3000--though, I did write and chart the song...😉)