ive completed my Demo and it basically plays out like a full game, I'm wondering if that is allowed? also I'm using music and SFX assets off pixabay which are not mine. is that allowed?

you should have the legal right to use assets for your game. That doesn’t mean you need to own the assets.

I believe sites like pixabay require some sort of attribution if you’re using some of their assets, but you should double check the license.