What do you mean "what happens?" Nothing "happens." You've probably elevated your blood pressure a bit, though. Coffee is also a diuretic and laxative. It can also make you retain water and feel bloated. So you would need to drink plenty of water and make sure you're hydrated.
But if you did this without knowing you were pregnant you've got nothing to feel guilty about. When you're pregnant and don't know it and you're eating and drinking things that are not recommended, well, that's kind of what you have a placenta for.
Now that you know you're pregnant you can cut back your coffee (or rather your CAFFEINE) to 200 mg or less of caffeine content per day. If you drink coffee for the flavor, then start drinking decaf. If you need "some" caffeine, start drinking half-caf. Learn to moderate and keep track of the mg of caffeine.
That 200 mg would include sodas/colas too, by the way. And chocolate.