Could she be pregnant ?

Me and my girlfriend had fun the other day , but NOT sex. I had 3 boxers on nd a pair of like gym shorts and there was a wet stain on the side. My girlfriend was on top of me with no clothes on but not the part were the stain was. What could the stain be ? Its the week for her period and she hasnt gotten it yet , is there anyway she could be pregnant ? Please help!