Just thinking. My clothes always get in the way. Is it okay to? Or am I more prone to injuries?

I go to a aerobic type of yoga in the morning before work, but there is no shower at the studio and I don’t have time to go home and shower. There is a room to change clothes at the studio.

i’m 15 years old and a girl. i’m kinda fat, not like i have to shop in special stores for larger clothes, but in fashion shops i’m always the biggest size if it does fit.
i’m starting a new school year tomorrow and i really want to loose weight, but i’m already chunky and kinda muscley and i really don’t want to be. i’m going to eat healthy, but has anyone got any pointers on that? also i’m gonna have lots of work but my friend said she’d go running with me, but would going running make me get even more muscley legs?
can you give me some tips on how to loose weight and what to eat?
and would yoga be a good idea?
i hate always being so self concious, and my clothes never fitting my properly, and so everyone eseeing my body. and i just want to be slim happy and healthy, help!
thanks.