I feel that I wasted my time in high school.
Do you feel unhappy when you think about this?
Well, I'm not perfect and I have made many mistakes in my life. It's okay, I learned something
I think these mistakes seem to have made you into a stronger person.  It's good that you've learned from them and I'm happy you've accepted your past.
Sometimes I still act like the bad boy I am deep down online. But really, I think I'm a good person.
It's good that you've seen you've recognized your past mistakes and are growing from them. You can forgive yourself for your high school mistakes and move forward with your life knowing things can get better.