Things to keep in mind:
-They may be judging you for traits other than exactly what is said - such as, "How do they carry themselves? How do they think through situations? How well spoken are they? How well can they communicate a thought? Did he/she learn anything from their experiences/school/whatever?..etc" So, even if you feel like you said something off - they may have been look at something else anyways.
-It is hard to judge yourself accurately! Look at old threads like these to see what I mean:
http://forums.studentdoctor.net/showthread.php?t=787423
http://forums.studentdoctor.net/showthread.php?t=607285
-Your interview is only ONE NUMBER they add in to your entire application score. Even if you MAY HAVE done poorly (you probably did better than you thought though!).. your other positive factors on your application can override it in the end.
-Your impression of the interview will change over time - You are probably only remembering the bad aspects right now, Try to think of ways to improve yourself for future interviews and then immediately move on from it. Try not to over analyze it !
That is my advice. I said some ODD STUFF in my interview (I was talking about how upset I made some clients.. and then never really concluded my story in a positive way. It was almost like I was just complaining about the clients or something !! ugh!) - But, I got accepted!! So, try not to stress too much and good luck!