Your phone number should appears in Settings>FaceTime>you can be reached by FaceTime at. If the phone number does not appear in there, you probably have to start all over again by turning off FaceTime and signing out on the phone before to can add the number back to the iPad.
This support article talks about it in detail and the most pertinent information for you will be at the end of the article.
THANKS FOR THE REPLY DEMO.
I just talked to Apple support. Here's what they told me. Because iPad is not a phone I can not associate a phone number with FaceTime / my Apple ID.
I can for example, call my son using his iPhone phone number, but he must use my Apple ID to make a FaceTime call to me (even though I have a phone number on my iPad).
In general, someone with an iPhone will associate a phone number with their Apple ID and it's used with FaceTime. Apple IDs set up for iPad owners WILL NOT ACCEPT a phone number as part of the setup so FaceTime uses the Apple ID.
This is copied from the support article that I linked for you above.
With iOS 6, your iPhone telephone number is linked to your Apple ID when you sign in to FaceTime or iMessage. This allows you to use your iPhone number with FaceTime and iMessage on other iOS devices with iOS 6 and on Macs with OS X v10.8.2 or later.
It doesn't say that the other iOS devices must be iPhones. This is a feature that was introduced in iOS 6. Read the article again and give it a try. This was written just as iOS was being talked about. This explains it as well.