All nearby test centers are full. What should I do?

I’m on the registration page of CB for the June SAT II subject tests. My preferred test center (my school) is out of seats, and all nearby centers are either not administering or also out of seats.

I know that my school may have extra tests and that if I contact my school and request standby, I may be able to take the test. For now, what should I do about my CB registration? It’s not letting me select any testing center within a 2 hour radius. Should I hold off on registration? Request a far-away test center?

Any help would be much appreciated!