What site did you use to register? Was it the scene? If you are having trouble there, then try our club's site:
If you pre-reg'd for Sat you can sign up for Sunday then and still avoid the day of fee. I am also going to be at the park Friday after 12pm to get the pavilion ready. Also it hasn't filled in a couple of years, but pre-reg has been really been picking up the last few days. Guarantee a spot and don't worry about not getting in by pre-registering!! Not to mention it would make my life easier to be able to set the leader board ahead of time.
I also want to point out that the Lumberjack Open (March 10th and 11th) is at Robert Morris this year and all pre-registered Ams will get a second disc in their player's pack!