If you look at the NYU website, it says that once you have been accepted, you are bounded by their contract saying that you must accept their offer or pay a handsome fee of $3,000.
On a serious note, call/email the school and tell them you are withdrawing. Isn't that common sense?
I just talked to NYUCD Admissions and they don't do a background check for their students. This is news to me, considering I originally received information from the company to fill out my information, and NYU was one of the schools listed that participates in the program supposedly. However, I guess I received the instructions initially due to acceptances from other institutions, which I have since declined. The reason NYUCD doesn't was stated as "it's a lot of money and time." Fine by me, that's money saved!