Hi Tammy,
What happened is when you went to the custom URL you had not set your profile URL yet so the information you input was applied to your profile.
So if you go back into
http://facebook.com/username again you will see a link that says:
"Set a username for your pages"
Click that to set the URL for your fan page.
Now that you have set the URL for your profile you cannot change it, just so you know
