Yeah I got an A and have got 98UMS in C2 90UMS C1. You just have to put in more work, but if you enjoy maths, it'll be much easier because the topics in A level are actually interesting and relevant. Be prepared to work through the textbook outside school and ahead of the lesson and you will improve by a lot within the first few weeks, it doesn't matter if you got an A*. I have friends who mocked me for only getting an A when they got A*s and I am beating them by a lot in A level. I became good by working hard so you can definitely do the same and go on to get an A* in A level.