Anxiety over reaching my offer

I've got an offer from Oxford but have genuinely had so much anxiety over achieving my offer. I got ABB in my recent mocks but need A*AA and I'm terrified that I won't get that in the real thing. I just keep stressing out over the worst case scenarios like getting a B on results day and I'm worried that I won't be able to enjoy my summer because I'll be scared about whether or not I reach the grades.

I'm at the point where I feel like its impacting my work- does anyone have any tips about getting over this anxiety, or reassurance that I can reach my grades with the mock scores I got?