Im 12 and feel over weight?

Hi. I am Brooklyn. I will be 12 next month. Before school was out i would be bullied about my weight. A very skinny boy named Cameron said i need to join a weight watchers club. Last time i checked i weight 102 pounds, but i think i gained weight since then. Summers here. Im scared to wear a bathing suit. Dont laugh, but im scared to run because the bigger you are the more your stomach "bounces" as my friends say. Im embarresed to go out in public. Please help! Any tips? I am tired of this! Also, im over 54 inches, but not by much.