how do you check on enrollment?

Michaels teachers: How do you check on class enrollment? The reason I ask is because there was a mishap today and I’m wondering how to avoid it in the future. I had classes scheduled for 9:30, 1:30 and 4:00 today. When I called at about 3:30 pm yesterday to see if there were any students, I was told that there was 1 student for 1:30. I asked a couple of time to clarify that there were no students for the 9:30 and 4:00 and was assured that there were none. At 10:00 am today, I got a call that there were 3 students waiting for me (1 pre-registered and 2 paying on the spot). Well, I didn’t have any handouts, nor my equipment ready, so I asked that they be rescheduled. Of course, I hate to see disappointed, unhappy students, especially when it’s not my fault. So, how do you check on enrollment and what is your policy about students who sign up “on the spot”? I don’t believe it says anywhere that pre-registration is required but, really, that would only be fair to the teachers, don’t you think?