It's hard to say what you did wrong. How do you feel your interview went? Were there any questions you stumbled on, or any part of your application that they asked you to speak in detail about, that maybe you did not answer to their satisfaction?
Sorry about your rejection, but it could be anything. Many professional schools will give feedback on what you can work on in your application, or where you might have fallen short in your interview, if you contact them...usually after the interview season is best.
It is not too late to apply to other schools. Good Luck!