Sometimes you go above and beyond, but it's still not enough to please a patient. Your role is just one aspect of the care a patient will receive when they go to the doctor or the hospital. That being said, you can still make a difference. Recognize that you have room to improve and that there is always an opportunity to grow from an experience. Even if you were not the one to cause the patient to have a bad experience, you can still learn from other people's mistakes. See everything as a learning opportunity! Express that to your interviewer!
"Is there anything I can do to make you feel more comfortable next time?"