I still have three triangular scars on my calf
How did you get those scars?
I cut myself with a knife several times when I was 18 because I was pissed about my dad
You should do your best to let your wounds heal. Even if you're upset with someone you shouldn't harm yourself. Have you thought about talking to someone about why you feel like this?
I've been through therapy. I don't want to talk about it to anyone. I just want to hide my scars.
I'm sorry to hear about how your dad treated you, but hurting yourself is psychologically damaging as well. It's fine to want to hide your scars, but don't hide from the world. There are good people who want to be friends with you and you won't be able to find them if you stay in a shell.