Thank you for posting!
As I am sure you will agree, we have never called a poster "immature" for asking these kinds of questions even though we have answered thousands of them! Mostly these questions are due to a lack of sex education and being too young/not ready for sexual activity. Your question is the same as many others but we understand that some readers want personal answers.
Pre-ejaculate itself does not contain any sperm. Sperm may be inside the urethra if a man ejaculated recently and did not urinate since. If he urinated since he last ejaculated, there is no sperm at all. Pregnancy is very uncommon from pre-ejaculate and the urethra would have to contain sperm at the same time. A woman would also have to be ovulating and engage in unprotected intercourse with ejaculation.
Prejecualte is very light and a minimal amount. It cannot pass through both underwear and denim. Sperm is really quite weak outside the body. It's far more likely that the "wet spot" was your own body fluids. Either way, no amount of touching it and then touching yourself would get you pregnant because as you said, there was no skin to skin contact.
Even when a woman has full, naked, unprotected sex, her risk of pregnancy is only about 20%. There is no risk at all for you.