the chances of pregnancy
are less because,
-in case of regular periods you had intercourse on 24th day of your cycle, so by that time ovulation might have happened.
-as you took i pill
within 72 hours, it will give protection mostly as it is having only 1% of failure rate.
-as your boy friend withdrawn.
but can't say that there absolutely no chance to pregnancy, you better check once with urine pregnancy test in case of missed period.