Not a huge amount, unfortunately, as you'd only taken one day's worth and generally speaking on the combined pill (I believe progesterone-only pills can be different) it takes seven days for you to be protected (assuming you don't miss any pills.) It is CONCEIVABLE that you might have already ovulated/ovulate in the next day or so in which case yes, you could get pregnant. However, my understanding is that it should be very unlikely for you to ovulate - but, possible.

If it's something that's going to eat you up, take plan B. General thinking is also that a pregnancy test can be considered fairly reliable from about 19 days after the sex in question, so you don't have to wait quite a whole month if you don't want to!

Hope everything works out for you.