how to stop thinking about a past exam?

a lot of negative thoughts come to my mind I overthink the shit out of it, and my university didn't release it today, meaning we will not see the grade until after the weekend but I can't stop thinking.

the problem is I have to study for another exam, but my brain just won't stop being so negative.

I know that it's in the past, and there's nothing I can change but my stupid brain wouldn't understand I have a history of doing bad on my exams, but on this exam I studied so much, and I felt good about it, like I solved a lot on it, but my brain keep thinking of the worse situation possible what if I fill the OMR sheet wrong? what if I solved a question wrong or forgot some signs while doing the equations? (it's a math exam) how to stop this.

and focus on the present not the past?