Well, this isn't the first time i've seen this. (Really! I'll tell ya later...) Here's basically what you can do. Since you knocked her up, you can pay for her abortion. I know it sounds crazy, but this is probably your best course of action. If she hasn't toldher parents already, formulate a plan of action, to get yourselves to a doctor, get an abortion (there are clinics that do it discreetly) and forget about the whole thing.
IF she is against the abortion idea, here's your plan B: Tell your family what has happened. Openly, and without shame. (Also, retardation has a higher chance percentage when a brother and sister have offspring, NOT cousins) Tell your family, and plan on getting hitched at 16.
All i can say dude, is you've probably chopped off about 10 years of your life. Fatherhood really shouldn't start until 25. Good luck homie.