And many junior high school leagues use high school knowledge. I think it's good for you to learn math well and win the first prize. Of course, it's my personal opinion, because I only won the first prize in the second day of junior high school or gave up studying later. Because it seems that the bonus points have been cancelled.
Anyway, I'm telling you as an experienced person. If you want to study mathematics, you should preview high school mathematics in advance, and then do high school questions or previous difficult competition questions. The more you do, the stronger you become. Ask the teacher about the book. After all, this kind of thing is different every year.
I hope you can get excellent grades.