It's true that I don't know who you are or what you did . But I know what it feels like to only remember the bad stuff . I seem to only remember all the mistakes I've ever made and bad things that other people have done to me. I try to remember things I've done good and I know there are plenty but those memories never stick out or repeat themselves over and over in my head like all the negative things do.
If you try very hard could you thing of some good things that you've done ? It may take a while to think of them if your thoughts are focused strongly on what you think you did wrong . But when you do think of something maybe you could write it down . Then maybe tomorrow you could think of another thing you did good and keep going making a list. Maybe whenever you are feeling bad about what you did you could read the list out to yourself .
There are many times that I think I am bad . It is usually when I remember something , a mistake I made. But I try to tell myself that a truly bad person does not feel guilty or regret mistakes they made. So if we feel bad about it and dislike ourself for it then maybe we are not bad but we are human .