Chances of me being preggers?

okay, me and my bf have had sex for the first time last sat [16 of sept 07] and we used protection , it was my first time ever having sex, buttt, im worried to hell about it, im only 16 and i cnt get a test or anything coz my maw might go ape at me if she see's it. I asked my mate about it and she said that it was my first so im just paranoied about it.
so what are the chances of me being preggers?
%-)