How do I get a sharper jawline?

Im 14 (f) 5’7 at 51 kg, i dont think thats overweight? I’m not skinny, and most of it is stored in my stomach naturally. I exercise in PE class that’s it, I lift weights for arms, rarely. I also take thyroid meds, so could that be a factor? Do I need to diet? Most of my diet is white rice, Asian too, so that could be another reason? I have braces so I don’t think asking an orthodontist for help would work (idk) I’m really insecure and need help!!!