I understand that with most birth controls, including this one it says there is a 7 day period that you should you a backup method.

I waited 7 days and on the 8th day had unprotected intercourse, my doctor told me that I should use a backup method for the first month and after I called and explained the situation told me not to take plan b and to continue my birth control as usual and to take a HPT in 2 weeks. What is the likelihood of becoming pregnant?