Hey OP, it sounds like life is really tough for you right now. I'm really sorry. I've been there before and, at the risk of oversharing, I hope you might spend a few moments indulging a random stranger's personal details that are being offered to illustrate a point:

Shortly before my 21st birthday, I found out my dad had terminal cancer, I got into a horrible fight with my girlfriend at the time (cops showed up. no charges, arrest, or jail time, but still), and I lost my shit and ended a longtime, close friendship.That was 20+ years ago.

I still remember feeling, at those moments, how much I wanted to disappear. Not necessarily die, but at least disappear. Go where no one knew me. Start over. It took a while to come to terms with that feeling. Life didn't allow for it.

One day after the other, I eventually made peace with my dad's death (I still miss him every day), made amends with my old girlfriend and friend, and, most importantly, made peace with myself.

I don't know if cutting yourself was genuinely an accident or not. My point is that you cannot make the changes you wish you could have made if you are physically hurting yourself. I do, however, get why you want to go back and change everything. As I'm sure you, you cannot change the past. And as hokey as it sounds, the future CAN be changed but that requires you being present to make it happen.

Please take care of yourself.

(Edited to fix my shitty typos.)