I'm On Birth Control (pill) I Have Been Taking It

I'm on birth control (pill) I have been taking it 3 months. I started the new pill pack Sunday April 24th. I took the first 2 weeks. I had unprotected sex Saturday night and I took my pill Sunday so that was the beginning of the third week today I lost my purse I carry my pills in there so I won't be finishing my pill pack. What's the chance I could get pregnant from missing about 6 ACTIVE pills before I would have started the placebo week? Should I do the plan B pill or is it to late ?