Is this cheating?

If you look at past papers to revise for a mock exam, is it cheating?. I recently had exam week and got a feel of how my real exams are going to be like. For my biology exam, I revised using my revision guide and then did past papers. I looked at the mark scheme afterwards to see how I did and how I could've got more marks. After looking at the mark scheme there were still questions that I didn't understand the answer to so I left them out. One of the past papers that I did happened to be the exam that I did at school. I got an A*. Do I deserve that grade?

Ok, let me try to understand this correctly. You did past papers for revision, but one of the past papers happened to be your mock exam paper right?
If you didn't know beforehand what questions the mock exam paper was going to have, then you do deserve the grade.
I mean, you didn't intentionally do that past paper knowing that it would be used as the mock exam, so you aren't at fault. It's your teacher's fault for reusing a past paper. In fact, getting an A* shows that you have understood the concepts taught in biology, and that A* is due to your own effort, as it is unlikely that you would have memorized all the answers when you did the past paper, and transferring them onto the mock exam paper.

But I kind of knew that the exam was most likely going to be a past paper(because I doubted that my school would bother to make their own exam paper) so I did all the past papers for the biology unit the exam was going to be on and I focused mostly on the most recent past paper because I guessed that they would probably use that as the exam and I was right. We were only told which unit the exam was going to be on a week before so I didn't have enough time to revise properly(the whole unit using the revision guide, considering I had other subjects to revise for) so that's why I used past papers. I don't know if that, if I was to do that unit exam again, with questions that I hadn't seen before, I would do badly or not.

Don't underestimate yourself. Unless you memorised all the answers and put them down on the mock paper, it would be unlikely that you would have gotten an A* just by doing a paper twice. If you are unsure of your ability in Biology, just do more mock papers to see where you stand.