I would say to go into your internship with confidence. I was quite nervous to start with the firm in the beginning because I had not had any previous accounting work experience, but looking back now, I see that my nerves were for nothing. The interview process had been very rigorous, and after it was over, the HR team had made the clear decision to employ me. You must realize that even when you feel like you know "nothing", there is a reason why you have ended up where you are. Someone saw your potential, and took a chance on you. It is only right that you believe in your capabilities as they believed in you.