I'd time travel back to fifth grade. Oh boy, I do have a lot of advice I could contribute:
"You're going to suffer a lot, but it's going to help you see the world in a different way. You're going to become a hard person, but also softer at the same time, because you've struggled in life, and you always want to be there for people who struggle. You're not going to forgive - and you're not wrong for not forgiving. You don't have to be a saint and forgive those who wronged you."