If an "X" prints out on your receipt, proceed to the side of the nearest CBP officer. Make sure that your passport with the CBP sticker and the receipt with the "X" are visible. When he is done processing the current passenger, he will wave you over, in front of everybody else..

It may seem kind of awkward to cut the line, especially if there are a number of people. However, you had the sense to sign up for Global Entry, and they either didn't know about it or chose not to, so don't worry about it...