Joomla 3.3.6 / Matukio 5.1.3

I have a checkbox booking field that is a single box with the option "YES". I want users to have to select that box in order to make a booking. It's a sort of "Accept Terms and Conditions" type of box. If the box is left unchecked, the booking shouldn't be able to be made. I have made the field required but people are still able to make the booking without checking the box. Do you know how I could do this?