datetimepicker date change override

I have a datetimepicker (dtp) on my windows form
the user initially selects a date and then selects the rooms they wish to book
The problem i have is that when the user goes back and tries to change the date (i.e when they click on the dtp), i show a message box that states that changing the date will cause all the current bookings to be lost. Do u wish to continue? If the user selects yes all the datatables are cleared and the date is changed to the one the user clicked on before the messagebox was displayed. However when the user selects 'No' in the messageBox the date in the dtp still seems to change to whatever the user has pressed in the dtp!!

does anyone know how i can override the date change so that the date remains what it was prior to the dtp being clicked

thx