Putting Limits to a Booking Form

Hello everyone,
My name is Staffan Anderin and I run a tennis business for teaching in Croatia. I would like to know how to make a booking form that will have limitations set when a program is getting full for signing up.

I want it to be triggered so that I will not be overbooked in a tennis program. I have been trying to use forms from Wix app market but the problems is always the same, Putting the limits to my tennis programs. So, I do wonder if you could give me some suggestions and what to use for this. I am without knowledge when it comes to Wix code.

My very best,
Staffan Anderin
staffan@tennisholidayspula.com