Where can sperm be effective from?

Hey there,My girlfriend has recentely been feeling ill. When she went to the doctor they suggested she could be pregnant. She thinks it is unlikely and won't take a test. We haven't had sex but we have done everything bar it. the most notable, or, the thing I am most weary of would be when I ejaculated on her. I am worried as I may have came on the outside of her vagina. Another instance where it may have occured is when we rub genitalia the head of my penis usually enters the fore layers of her vagina, normally around the clit or sometimes lower. When this happens I am normally wet (pre-cum I assume).My question I guess is,                         Where is the furthest away place from the fallopian tubes that sperm could end up causing pregnancy ??Thank you.