Hello so I'm really confused I had bought the game but when I tried to download it, but it takes me to the final demo.  Is this the actual game? If not how to I download it?

Note that you only get the key for use on steam, not a game directly from itch

Use your code and redeem it on steam https://help.steampowered.com/en/faqs/view/2A12-9D79-C3D7-F870