Missed a pill... HELP

What are my chances of pregnancy if I missed my last actual pill (not sugar) of my pack? I thought it would be fine to use that as my first placebo/sugar pill day because it was just the last pill. So I still had four days of placebos. Everything went fine but then I had sex two days after my period ended. Chances of me being pregnant? He came in me.

I'm on my sugar pills for the next month now and I only have dark red discharge (on the fourth day of my sugar pills) and I think that might just be from having sex the day before. Other than that one day I've taken my pill perfectly. I didnt think that it would be a problem...but I guess it is.