Kells, it will be a really really big surprise if you are pregnant. The Plan B is just another very strong birth control pill and it will delay your bleeding week. Remember that you are not menstruating while on the pill. What you get is withdrawal bleeding caused when you get to the inactive pills. The hormones withdraw and viola, withdrawal bleeding. When you took Plan B you introduced a massive amount of hormones that will take about another 7 days to get out of your system.
Just start your next pack on time and keep supplies handy for in case you start to bleed in the next 2 weeks. You might actually skip it all together due to the Plan B and how close that was to your bleeding week.
Best of luck!