Shall I lose hope or not?

So I’m in year 13 right now. In my mocks I got an A in psychology, a D in biology and a C in chemistry. I resat bio and chem and got a C in both. I genuinely don’t think I have the…mental capacity to get A’s in the real thing. Especially for biology. I studied the entire summer I knew ALL of the content I did all the pmt questions and a lot of past papers. I don’t know what I’m doing wrong. No matter what I do I’m behind..apart from psychology. Maybe I should have picked sociology or smth else. I’m gonna start locking in from now but I’m not sure I have much hope.