Switching Tests Question

I signed up to take US History, Math II, and the Chemistry SAT II.
I have since decided to drop all three and take Math I Sat II instead.
Collegeboard has said I can switch tests as I please at the test center, but I would like to hear from someone who has done this.
Seems to me I get a book with all subjects, and I just fill out the Math I part, then leave after the allotted time for this.
I just wanted to confirm with someone who has done this.

Correct.