How well do you think you have performed in this interview today?

"Thank you for taking the time to meet with me. I feel I was well prepared for the questions you asked me today, and I am happy with my performance in this interview. Can I ask if there is anything I can clarify for you or elaborate on from today's conversation?"

If you feel the interview went well: 'Thank you for taking the time to meet with me today. I feel I was well prepared for the questions you asked me, and I am happy with my performance in this interview.' Then you can ask the interviewers if there is anything you can clarify or elaborate on from today's conversation.

If you feel you could have performed better: 'I feel that I was well prepared for the majority of the questions you have asked me today; however, I would like to clarify my answer on one particular point...' Then, return to the question you may have stumbled on and answer how you would have liked to answer the first time.