How can I possible turn back to God after self harming

The bible says that all humans are carved out of His image and we're supposed to be sacred temples that need to be taken care of, but i went and ruined myself out of rage. The only reason why I haven't stabbed myself in a limb or something yet is because it'll be too painful, so I stick to slices or hitting my head. Im only 17 and ive already messed up so much. Just typing this out makes me feel disgusting. Scars never fade, even if i did somehow get out of this muck and restart my walk with God i'd never be able to forgive myself. I feel like I already wasted the life that God just gave me

I have no parent to talk to and I cant stand that thought of my siblings seeing my legs because I know they'll tell my mom and I'll have no choice but to confront myself and everything I've held inside me for the past 10 years. Idk if I want advice or to just get this off my chest. I just dont wanna exist anymore