I was in the same boat as you when I was in high school. I dreaded swimming day because we were not allowed to wear t-shirts over our bathers - everything had to be the uniform. I would say that I was about 68 kilos then and in comparison to my peers - about 10-15 kilos heavier then them.
Be strong ... you can lose the weight. And with some great help, motivation and advice from the ladies on this forum - I feel sure that you can overcome your bad eating habits and truly shine.
Welcome aboard ..... and I ended up losing the "high school" weight only to regain it after each child!!!