I actually am in somewhat of the same situation now, I got her the Plan B pill though. And the girl isnt my girlfriend...=\ I definitely understand your worry though, its really hard. From what I've read, if you've ejaculated recently and have not urinated, sperm can be left in the folds of the penis. Which from my experience, sounds true. But I'm not sure that I agree with britbrat on this because its really hard to find accurate information on this topic most people disagree.. I think, common sense wise, precum would have less than an ejaculation, simply because it contains the LEFT OVERS from a previous ejaculation. Logically, this cannot be more. Also, from what I have read the chances of pregnancy during ovulation reach as high as 30 percent...a 1 in 3 chance. However, that is from actual ejaculation. From precum, I would say the chances are slightly less, simply because there are less sperm. I would say, depending on where she is in her cycle, anywhere from a low 1% chance( if it was after ovulation) to tops of a 20% (1 in 5) chance. Good luck. I feel your pain.
i actually just did a bunch of reading up on this for my own personal knowledge.. similar situation you could say.
they are higher because there is more sperm in your precum if you've gotten off in the past 2 days or less.