So let's start with FAQ that no one adds to help me or anyone in itch staff.
Is your account a direct payment or collect-by-itch?
If your account is direct then you must handle all taxes, it is never recommended to use this feature for inexperience tax users.
If collect-by-itch you need to follow instructions to fill ITIN and then you fill out tax treaties.
Did you fill out incorrectly by saying you own a company or you do have a company but don't know how to fill it out?
By saying you own a company, you are to follow any additional taxes it may come with being a company. This is never recommended without a tax expert to help you. There are too many laws to follow when you become a company and selling games through the internet.
If you are not a company, you should fix it. I am assuming you are the only one with no other person, meaning you do not have a employee. Agreement/contracts are different matter. Partnership may be a reason for the tax but I do not know if you are in a partnership. So saying all this i am assuming you are working alone which under UK is called https://www.gov.uk/set-up-sole-trader
Even if you are in the UK, you still need to fill out the tax treaties because US requires it or you can lose a lot of money.