Majo,
Sounds to me like you are pulling a serious headtrip on yourself girl. I bet you don't screw up as badly as you think.
It's ok to make mistakes and people will forgive them. You can ask - sometimes you can even not ask and they will forgive anyway. One mistake or 100 does not make you a bad person. Your wariness of mistakes and desire for forgiveness demonstrate your sense of conscience. People who are truly bad lack conscience.
If you think you are a bad person, though, it is easy to think that is what others think too.
If you can't help feeling like you are bad, could you see that as a judgment? Consequently, what if I asked you to suspend judgment on yourself? Could you try that?
I am saying, if you cannot believe you are good, then how you draw the line at believing you are however you are. (Yes, even circular logic occasionally has its uses.)
waves
p.s. The rapid moodswings are a borderline trait... but often in borderlines they are triggered by thoughts and perceptions. If you adjust your perceptions, you can nip the moodswings in the bud, or at least reduce their intensity.