I'm freaking out, but I'm not sure I should be.
My girlfriend and I were fooling around a week ago in her car and I'm scared to death that there was semen on my hand when I fingered her... If there was (a very small amount, if any), what is the likelyhood that she could be pregnant? This is so horrible.
The odds are remote that a tiny bit of semen on your fingers can get her pregnant. A few lone sperm in the vagina are quickly attacked and killed - it takes a "blob" of semen to make it way through the vaginal defenses. This is not to say it is impossible, but quite unlikely. Still, diseases can be passed via fluid fairly easily, so you should also use good hygiene.