Hi @Sheena21
I am not entirely sure what the problem is, but if you want to cancel a booking, call the company. This site is a group of Airbnb members who trade tips and advice. We have nothing to do with bookings/cancellations.
Just an FYI, unless your guest will be breaking rules , or your are seriously ill, or there is some unforseen problem (flood, fire), you will be penalized for the cancellation. However, too many people in a room would be considered a legitimate reason.