I'm a bad person.
Why do you think you're a bad person?
I've done bad things in the past.
It's good that you can acknowledge that you have done bad things in the past, but you should not continue to do them. You should try to actively make changes in your life to do good things instead of bad. It will make people like you more and make you happier with yourself.
A bad person is always bad.
That's simply not true, people can always change and improve themselves. I encourage you to do the same.