plan b week before my period.

My last period was September 24th and lasted for about 4 days. It's my usual cycle. Yesterday I had sex, and of course we used protection. Being not on birth control, I still kept thinking about what could happen. I did get alittle scared so I decided to go get plan b just to be on the safer side. My period should come soon but would taking the pill before my period screw up my cycle now? Will I still get my period at the right time or later? Please help!!