weight and friends

Ok so i’m 5’8 and 14. I weight 140 ish some times over sometimes under. I play soccer and I’m pretty active. I’m not fat but I have like kinda big thighs. Anyways, my friends are all shorter than me around like 5’4-5’5 ish and theyre all super skinny all under 120 and whenever anyone brings up weight i get all anxious and just say i don’t know how much i weigh. Is anyone around my height and weight that has tips on just being more toned and flattening my stomach?