it's hard to get answers on the board last minute - most of the CRs ship out for the weekend Friday afternoon.
IF there are spots open, the director will likely accommodate your situation and let you purchase a membership and register at the same time. but you're taking a pretty big risk driving to the track without a spot, and you will pay the late registration fee.
for your sake, I hope you stayed home on Sunday. Not the type of experience you want for a first event. 3(ish) sessions, and then a monsoon.
I promise it's usually a lot more fun!