Is UK size 12 fat???

Dani
So I'm wearing a UK size 12 is that considered fat I'm a 15 year old girl and is about "5,6" and I weight about 11st 6lbs and I feel really fat and I don't know how to lose weight I've tried everything I hate being this size I feel like I'm too big for my boyfriend as if he deserves someone better and skinnier like he is