What do you do when you are not good at your job?

I tutored two students for exams this month and the results came out. While they didn't fail, they werent happy with the marks. They barely passed and totally not happy with me. I was shocked myself, since my previous students did well. The guy who suggested me to the students felt humiliated because they had to pay a good amount of money to me.
I'm returning the money...but my confidence in my skills shattered entirely. They were my second batch and now I feel that I lost my web of connections already.