The actual idea of a platformer where you are swapping between 2 different versions of the level is legitimatly a very good idea.
I understand that you're aware of the difficulty issue so i won't say much on the matter, but it is a shame because i would have loved to have seen more of it! Hopefully playtesting with others is high up on your list for next time! (hmu if you need strangers to test!)
Now! Besides that, like i said i think the idea is genuinely very good and the atmospherics/artwork and the storytelling i was able to see were very nice.
Honestly, think you've done a good job for your first jam. Nice work!