I'm on diet and am in desperate need of some "fat burning" workouts & advice!?

I'm 13, and I'm not overweight but I am above average and deffinitely not thin. I'm going the healthy way and want to add some really good workouts to my regimen. I can't exactly buy anything that is obviously a weight loss tool because my parents would think I'm an ego-obsessed freak...however I do already have a heat building yoga workout. Are there any online free videos/websites that you know of? Are there any poses? I just want to look pretty for my graduation =] Thanks