How do I get good at P.E.?

I'm year 7 in High School and I've never been good at PE. Never. But, I really want to, and I do try. It suddenly hit me when we were doing discus and my PE teacher said to me and this other kid "You two face forwards unlike everyone else please because I don't trust you." and I felt pretty upset. Also, there is a person in my class who I want to make friends with and she's really sporty and I'm too shy to make friends with her and I wanna be like her (sporty). Do you have any suggestions on how to get good at sports and PE? P.S. I do karate and dance outside of school. Thanks! :)