I agree with the things Bob has said. These things can take time. How many students do you need in order for this to be worth it for you to run ?
If you get calls in between now and your camps,
DO NOT TELL THEM THE CAMP IS CANCELLED (even if it is) !!! You tell them that there are no longer any spots available, and that you will place them on a waiting list and if a spot opens up at the last minute, you will contact them (and then you wait until you get more than the right number of people to run your show).
At this point, I would recommend *not* actually enrolling anybody else and instead, place them all on the "waiting list" until you are POSITIVE that you will have enough enrollment to run the camp. Also, this way you will have their information to do some individual advertising next year, too

(email addresses

).
This is important because all of the advertising you have done this year, even if the camp doesn't run this year, will still serve you well in the future if you handle it correctly. No matter what, treat this camp as something very valuable (people
want to get something valuable).
As far as advertising goes, there is not much that can be done about this year. But, I have a couple of ideas for next year.
A general rule of thumb is that people want to feel like they are really getting something "special" or, at least, what they have paid for. And, we, as teachers, need to help them realize that they are. One way to do this is to create some sense of accomplishment for them, by them just having been able to enroll at all. Putting something like this on your advertisements :
"Spaces within the camps are limited so please contact us early to reserve your spot !"Will create a stronger curiosity than this : "Enroll today !" -- while
we may think there is some sort of excitement in that, most people are procrastinators (!!

!!) unless they have a wee bit o' fire under their bums. You need to help them feel motivated by giving them some kind of deadline -- "enroll today" is too open-ended and doesn't impact them the same way. "Today" could mean tomorrow ... or the next day ... or next week ... or next month ... to a lot of people.
Also, you may want to include on your advertisments some kind of photo that represents what would "happen" in the camp. A small group of kids at the piano, or even an individual one (you can use your private students for this -- or even the 'kid next door' if you don't want to use your private students for this). Photos can work wonders when one is wanting to authenticate any circumstance.
Don't give up altogether if this is something you really want to do. Just concentrate on improving your efforts in whatever way you can.