Scars

If you can't give up the cutting thing, maybe try something similar??
This is kind of an oddball answer.

If pain is your release, maybe getting a piercing would help.
I could see it like this... You're feeling like cutting yourself. DON'T DO IT.
Wait and get a simple piercing. Like your ear. You want it to hurt? Try some of those unique cartilage piercing. Tragus, Conch, or the basic. It will be hardly noticeable.
Yet a piercing can still be a reminder to you of what was troubling you at that time. You'll never really forget what bothered you. But Scarring your arm doesn't make it better. Once your over it, take the piercing out. Long as you don't get a crazy eyebrow or lip piercing the scar won't be noticeable over time.

Really don't think you can change who you are, just try to make a positive action out of those negative thoughts.

I have severe pitted acne scars and it is one of the main sources of my anxiety and depression. People have called me out on my scars and called me ugly because of it, well also because I AM ugly. I can't get over them and I can't stop obsessing over them even if I see other people with acne scars living normal happy lives. The torment in my head wont stop and looking in the mirror is painful.