Double-booking with Google calendar

Website owner, Debi, says this:

I was playing with the calendar to see how it was set up with the different services. When I left the buff mani service and put in other services, there were no appointments showing up on Feb 21 again. I booked an appointment on the calendar to see if it would go through, and it basically booked that appointment on top of the ones already there. Now on google calendar, I am double booked.

We need some help getting this to work properly. Thanks!
Adelle, / web helper