Can I get a girl pregant if my pre-ejaculation gets on her pants?
Pre-ejaculate fluid can contains a few sperm cells. Not a huge number, but enough that the possibility of pregnancy exists if the sperm is able to reach the vagina. Cloth is not a barrier to sperm. But in order for the sperm to reach her vagina, there has to be enough moisture from your pre-ejaculation to both wet her pants and underwear. The likelihood of that happening is not very high. Hence, overall the odds are so close to zero that you might as well consider it zero.
But this then leads to another question: If you are pressed against a girl for so long that your pre-ejaculate is soaking through both your pants and hers, then you are staying too close and both of you are getting too sexually aroused to make good decisions. If by dripping you are implying that your penis was out, then again we are talking about improper behavior because you should not be exposing yourself to a girl.