When did you buy it exactly? You should've received an email from Itch with a download link. You might've typo'd your email address if you never received an email. It would be good to get into contact with Itch.io's support in that case.
Hi, I didn't typed the wrong email address.. when I filled it in I get the error that my credit card is not valid. but the money is gone from my credit card. I can show you the image that I paid...