How do I get good at sport?

Ok, i'm 13 years old and really unfit. Now, im not fat, im slim. I come last in long jump, high jump, races, swimming, hurdles, javeline, shotput, discus, rounder,netball..... im bad at flippin everything!!!!!! i get teased!! pleaaseee i need help. How can i improve???????? answer ASAP!!!! its sports day in 1 month!!!!!!!!!! ( be detailed if possible) thnx xx :-)