One possible version:

Dear Jim,

   I’m writing to tell you my exciting plan for the summer holidays. I intend to join a Dragon Boat Training Camp.I wonder if you’d like to go with me.

   This camp will open on July 20^th. It offers teenagers, like you and me, a chance to enjoy sports and learn about Chinese culture.If you are interested in it, let me know and I’ll send you more information.

Hope to meet you at the training camp this summer.

 (https://www.geilien.cn)

Yours,

Li hua