It isn't easy to judge your own mathematical ability. Good marks in mathematics are certainly a guide; it is perhaps even more important that you should enjoy the subject.

The best prerequisites for achieving a degree in mathematics are curiosity, the capacity to enjoy logical thinking and an intellectual challenge, and a substantial element of determination. Armed with these, you will be ready for everything - even for the mathematical difficulties that occur from time to time, and which may at first sight seem insoluble.