I was playing with my girlfriend i had my underwear on while she was naked... she was very wet and sat on my lap ... i was wearing an underwear and i didnt ejaculate only precum is there any risk of preganancy?

Not really, but...: Sperm do not swim through clothing in real life, so keeping the clothes on is good contraception. Wearing jeans with a tight button fly, that are really tough to unbutton, and a tight waist to stop hands from slipping through, is good contraception. Of course, a sure way to prevent pregnancy is to never be alone with one another (safer to be in a cafe, public library, or among friends or family).