If it's a pre-order, it won't be in your library until it's released. What normally happens when you place a pre-order?
If you've placed a pre-order before and this is acting differently, you might try asking somewhere in B&N's forums at
http://bookclubs.barnesandnoble.com/ (I'd guess either Nook Talk or Ask the Community or maybe one of the Support boards towards the bottom). At least one of the moderators is a B&N employee (I think they all are), and answers this sort of question all the time, and can get in touch with people who can dig in to your account.