Am I overreacting?

I'm 17 years old and I weigh 260 I'm always told I'm really fat and overweight and my sister and friends tell me I'm not that big but Im not delusional I know I'm overweight I just don't know if I'm huge or not I know my stomach is kinda sucked in it's hard to not do I've been doing it my whole life I used to be a lot bigger when I was younger and it was a habit I know this probably is the right subreddit for this but idk man I just feel disgusting and I need an answer