Help me please

I’ve been a prisoner to both my body and my insecurity for 18 years. I’m not morbidly obese but I’m bigger in the tummy than most girls my age. I’m too embarrassed to wear what I think is cute and I don’t have to confidence for certain social situations because I’m scared people will look at me as the fat girl.

I’m at the beach right now and my tiny friend keeps posting pics of me and I look huge next to her. Last month my grandfather offered me 100$ to lose 30 lbs and a little kid in the pool just asked me why I’m fatter than my friend.

I’m tired of being scared that someone is gonna call me out again. I want to lose weight but I lose motivation with different exercise plans and diets - I just want to love myself but I need help. Please give tips