Don't hold onto anger. Don't blame others for your mistakes. Apologize for your mistake, learn from it. From that point on, it's really out of your hands.
Ask yourself this when someone says you can't do it. What's holding you back? Exactly. Nothing but them and you, but only because you are letting them.
Dear Self. You know what they say about perfectionism...don't you? Why you don't have to be perfect, and in fact it's necessary that you don't try to be.