I definately know where ur coming from. I'm 19 and am about to become a single mum in 3 months with my first baby (i'm due March 12th) and it's pretty scary in a way. Just remember that you're not alone in this, and even though there will be times when u don't think u can do this there will always be people on this message board that are here for you - we'll be going through the exact same thing, so we're here to help one another.
No doubt you'll make some great friends on these message boards and find some people to talk to when ur feeling down and feel like everything is just getting a little too much. Kimmie has a great point - if we can go through this pregnancy alone then we have the courage to raise our babies.
If you need to talk then u can PM me or any of the other girls...Hope to hear more from you soon.
~Jess~