So, I got the game with my graphics card and i redeemed the code back in March. I have absolutely no idea how to get the game. It's not in my library and all this about a pre download which I also can't find. Any help?

and where do i go for this?

Go here:
https://www.gog.com/redeem

that's the thing, I already redeemed the code back in March and I was sent an email from NVIDIA, where I got the game from as a extra for the new graphics card, that said I already own the game. I didn't get any other codes to redeem.

When you originally redeemed the game through this website, it should have prompted you to log on GoG and the game should have appeared immediately in your library. What I would do, just go to the website I just linked and try to redeem your code again.

yea, no i've tried that and it says the code has already been redeemed, which it has back in march. after i redeemed the code, i got an email from nvidia saying i already own the game. Along side this, I went to the support page for nvidia and asked them, so now i'm just waiting for their reply. Thanks for your help everybody