Strategies To Lose Weight Fast

I’m to big for my age and my friends say I’m not fat but I’m thick. I know I’m fat and I recently joined weight watchers and I need another way to lose weight because I don’t want to be the fat girl that graduates. Along with being fat I have dark stretch marks how can I get rid of them?

I’m 5’2 and i weigh 120-125lbs and I’m planning to lose about 15 lbs. I don’t want to get any stretch marks if I lose a lot of weight ): How can I prevent from getting stretch marks? I don’t have any stretch marks right now.