Should i tell my parents?

i am a thirteen year old girl. i cut myself. and have for about five months now. only one person knows. the one friend was the only friend i didnt think would reject me or think im crazy. my parents will think im crazy i know they will... what do i do. and my friend asked me to get in the hottub with her and i didnt have my bathing suit and it was just us and she was like where your underwear and i sadi i cant. and i kept giving her excuses. do i have to tell her? i dont know what to do!!! i have thirty three scars. mostly on my legs. its almost like im getting addicted to it and im scared because i have very addicting tendencies that runn in the family. my dad has alcoholism and that what pushed me to cut and i dont know what to do. i need advice. i know someone can help. but i dont know who and how to get it. do i tell my parents? and my friend?- like i would to but i dont want ANYONE knowing. ANYONE!!! i will be known all over the school if i tell the wrong person and will have no friends. and ill just cut more. please tell me what to do!