A buddy of mine had this problem, and ended up winning her over to get an abortion with the arguement of,
"were so young that even if you do keep this kid, its life is going to be horrible while making ours horrible, you wont be able to go and do what you want with your life, your kid is going to be underprivilaged and not really have a great childhood like it would if you waited"
but really its sorta hit or miss with girls, if she wants to keep it you rfucked, but i dont really feel bad for ya man, they make condoms for a fuckin reason.
and p.s man, next time this happens that you dont exactly get out in time, go to a planned parenthood or some type of association like that in you area and get a morning after pill.