I think you have your own skills and plan to enter Dongying Sports School. Tell your family truthfully that dreams are very powerful.
You can tell your parents that school is a springboard. The goal after entering school is to join the national team and the provincial team. You can be a PE teacher at worst, and your future work is not a problem. You can also be a fitness coach and a sports brand agent.
Of course, I won't leave the culture class, but I will take several certificates during my study to give my family and myself peace of mind. This is another story.
You know what you want to do, at least let others know that you know, so that you will get others' support.