Plan B???

So I've been on birth control pills for over a year now, but tonight was the first time my boyfriend has ever finished inside me. I don't think I'd worry so much except that I accidentally started my pack a day early yesterday and so my period was cut a day short. Technically I guess it's an inconsistency in taking my birth control, but I didn't miss a day or anything. I'm torn between paying for plan B which I've never used just because I did technically mess up my pills. Any one have any advice???