Yeah, I agree that playtesting the game early is really important and if we were making a real game intended for commercial release, we definitely would take it more seriously and spend some time doing that. This one was just a tiny game-jam stuff only to have some fun. :)
I still think adding simple checkpoints that restart the level when the player dies would totally ruin the meaning of the game. Those fits perfectly to the hardcore pixel-perfect platformers like Super Meat Boy and Celeste, but this is (even though hard) still more some kind of puzzle one. Once you figure out what you have to do it's easy. This is why those two shortcuts IMO fits well - you're able to finish it in about a minute when you know where to go.
Either way, this is still just a little game-jam game and we don't want to spend weeks working on it more just to polish it. Doing other game jam or working on other stuff makes more sense. :)
Btw, it's not 1 single level. Every room is a single scene. The music keeps playing over scenes because it's a simple Singleton manager that doesn't get destroyed while a new scene is loaded.
Thank you again for your time and thoughts.