OPK missed it?

My RE wanted me to start on cd12 using my second pee of the day. I didn't want to miss it so I did the first and second. Everyday I'm getting a negative. According to my chart and what I know, it looks like somehow I missed it. It looks like cd15 was the day. I have a regular 30 day cycle. I was supposed to do an IUI this month when I got my "smiley face" but it is nothing but me being sad over here. Did I miss it? Do I keep doing the opk until my AF comes?