What's done is done, you can't do anything else about it. Things happen during an interview, you're nervous, you don't know what to expect, etc. It's okay. Take a deep breath and know that you're one step closer to your end goal. Try to go do something non-school related to take your mind off things.
Based on my experience, what you think happened vs. what actually happened is probably a lot smaller than you think. I really wouldn't give it so much thought to be anxious about it. Trust the process and trust yourself, deep breath.