Thats too bad they canceled on you. Did they give you a reason why it was canceled? If it was due to low number of people signing up, I'd find another place to go through. If I have a class scheduled, and only have 1 person sign up for it, I am still holding that class! It's unfair for the other people who had to likely adjust their schedules to get into that class.
Plus if someone were to call me up or drop me an email asking if I was free to teach a class on a non scheduled day, if I have the time, I'm doing the class. Even instructors gain something out of teaching more classes. More experience teaching, more time on the range helping others gain some experience, plus being more flexable adds some free bonus points for advertising. People with good experiences will tell others about the good experience. Its a win win situation for both sides.