It's not a big deal. Anything that happened in the past that you know is your fault is nothing, don't make it a big deal, it's just part of your growth.
If you remember some people that just use you in the past and you allow it even if you already knew it.. and it hurts you because you didn't do something about it, just let it go. Forget about it, it's just part of your growth. I know you can fight now, I know you can reject them now but now is not past. If you're not used in the past then you will not be a stronger person now.
If you remember a lot of things that could have been yours but you didn't get it because you let your fear take over... forget about it, I know your braver now, I know you are willing to face fear now but that's just the way it is. If you were not a slave to fear in the past then maybe you are a slave now. You need to experience those things earlier so you won't experience it now. Stop being regretful, it's just a part of your growth.
Stop remembering things from the past that only hurts you. You are lucky because you experience it, it toughens you, it hardens you, it just made you a better person.
All the bullying, rejection, failures, hardships, heartaches. Those are just part of your growth. Stop going back to the past and taking revenge. You are a new person now, you already grow. Just laugh at those things that hurts you because it cannot hurt you now anymore.