[Coffee.]

Agree with Elliotte.

I think you are getting mixed up with "ovulating" and "fertile". See, you are always fertile. For around two days of the month, you are ovulating, which makes you most fertile than the rest of the month. However, you can get pregnant on any day out of the month, including menstruation.

I would say it is a low chance, if it was only once, however, I would recommend you take a pregnancy and always, ALWAYS, use a condom.