Don't waste any time contemplating if you've done enough, just keep going until the day of your exam. Go through flashcards, dump out all the knowledge you have topic by topic on mind-maps, and Most Importantly practise past paper questions. Get familiar with key words the examiners are looking for, make sure you're managing to finish all papers within the time limit. Nobody can say if you're guaranteed an A with the way grade boundaries are calculated on the fly each year, but the more efficient prep you do in these last few days, the better equipped you'll be to confidently finish the exams. Good luck, you've got this!