Hello Good Evening,
can possible despite the pills because it is not 100% effective.
1-2 % failure rate is there.
But from now onward, you should keep watch on your period and repeat urine pregnancy test after 1 week. If UPT will be positive then you can go for USG to see gestational sac
and then only you will get confirmation about your pregnancy.
But meanwhile periods also can be started with some unusual delay.