Where are you from Yotoko?
You have to be one of the first 64 to pass the qualifying registration in your area (via the online test) to be able to compete, but anyone can go to take part in the other activities/get Celebi. However, one thing, I would say that if you really want to compete and you can't register anymore that you should go anyways and go *early*. Because I'm pretty sure a lot of people who take these tests and pass are not going to show up. So when the time comes they won't have 64 competitors at site that passed the exam and have their printed documents.
If you cannot take the test anymore I think it would be worth a try for you to ask one of the head staff members/judges to let you compete if they don't get their 64 competitors by the time the tournament is supposed to be starting. Gotta be there early for this though! I've entered a few other tournaments this way, sometimes you get lucky and they don't all show up.
Still though, this is last resort, would be best if you just passed one of the tests for the 4 possible locations near you.