Don't worry about the examiner. My friend just did her grade 7 RCM, and she couldn't remember how to start her piece. She tried three times and finally got it. The examiner still gave her a nice overall grade, too. An examiner is trained to see the quality in between the slip ups. I completely blanked on my grade 9 exam's technical requirements MORE THAN ONCE, and I still got in the 80's as my overall grade. And my teacher always says, too, no one's going to care what you got on your grade (whatever), exam once you have your ARCT. I don't know if you're going that far or not. Remember too, that even if for some ridiculous, out-to-lunch reason you fail the exam, you can still go on to grade 9. A grade 8 exam isn't even required. I never did one. The only exam you can't blank on is ARCT. People blank in exams all the time. Try not to worry about it while you're playing or else you'll just end up phsycing yourself out, and then you're more apt to make a mistake.
Take the practice suggestions given above, and remember, you can't do anything more than your best. We all have good exams and bad ones, and we don't get to pick which are which. Your mark is only someone's opinion anyway. Only you know if you played well or not, because only you and your teacher know what you are trully capable of, and we all have good days and bad days.
One more thing to make you feel better. On my list C piece in my grade 9 exam, I played over half of it (2 pages) WITH THE WRONG RHYTHM! My eighth notes became sixteenth! And in the half that I counted correctly I messed up on the climax, and didn't recover well for a number of bars afterwards. I still got 7.5 out of 10 on it, because she could see that I played it with an overall sense of feeling, technical ability, and security. (I was sure my rhythm was right, lol). They look beyond the mistakes, to the music. Yes, I lost a few marks for the goofs, but not tonnes.
Hope this cheers you up.