Thanks for the feedback! The 2 bugs you stated are definitely things I'm trying to fix but wasn't able to before the end of the jam. I also agree that it should be more clear that people should collect the screws after getting the key and is something I'm considering in a future update.
With the rewind, I saw it as the factory "rewinding" (like unseen gears and stuff that make up the factory now moving in the opposite direction) that make some platforms disappear and reappear, as well as things going in reverse or stopping altogether. Time also rewinds in a sense that collecting the screws before the key removes the screws from the score, and you're being rewound to when you never collected any screws in the level.
I definitely wanted to add some sound effects, but I didn't have much time left (Although I'll definitely check out BFXR for some of them).
The player is just a white ball because [SPOILER] it gets disappointed after learning its true identity. Although I can see why it would be weird having a plain character inside of a more detailed area.