I think you did it right--if you log onto the nbme website and click "step 1 and step 2ck scheduling" you can route yourself to the "confirm your test option" on the prometrics website. Enter your conf # and the first 4 letters of your last name and your info should show up.
This has me worried now. I can't figure out how to get to the confirmation screen on Prometric, but when I get to my scheduling permit on the USMLE site it says my test date and in parenthesis, "Scheduled."