Can anyone help?

Hello. I am an As student and work very hard in biology. I am with OCR and was getting A/B in all of my mocks (I did every past paper). I was really excited to open the paper but when I looked I saw a big E staring at me. The exams went so well! Am I just stupid or has the exam board messed up my grade? I have paid to get my papers back and hopefully appeal for a remark. My friend also Had the same happen to her. Can anyone explain?