Dear Jack
I am sorry to hear that you haven't decided whether take part in the school maths competetion or not. I think you'd better take this chance because it's a good oppotunity of exercising. Second, you are interested in maths and you are good at maths,too. So don't worry about it too much. Third, if you take part in the competetion, it can help you get more knowledge and make great progess. So take this chance at once. I am looking forward to hearing from you.
Yours
Li Hua