I'm no expert, and I have no data, but still I'd say there's about 0.0001% chance you're pregnant. The chance of a) one of whatever small number of sperm are in his pre-ejaculate getting through your underwear, into your vagina, all the way up your vagina, into your uterus, and connecting with an egg, while at the same time, b) your birth control pills have failed and there is an egg there, and c) it is exactly the time of your ovulation and your egg is ready, is extremely, extremely small. Besides that, a fair percentage of zygotes and embryos don't even survive their early minutes, hours and days.
If you really feel unsure, you could take a pregnancy test (not sure how soon those can tell, so you'd have to read the box, I guess), but really, I'd say the chances are very, very low.
The chances are low with dry sex; the chances are low without ejaculation; and the chances are fairly low even having full-on consummated intercourse while on the pill (which is the whole point of the pill!), so really, well, you get that point.
So, don't worry, be happy, and if you ever do get pregnant, and you don't want to have a baby, PLEASE don't keep it! Thanks. :)