i dont know which location u r going to. but i have heard that the 'guard' at the entrance decides whether to allow u in or not and one of the things he looks at is how much is the 'crowd' in the room. just to better your chances, i wud suggest go early in the morning whenever your local CIS center opens. hopefully, not many ppl wud have shown up and thats one less thing to worry abt.
good luck!