You should have thought about that earlier! When I can't sleep and need to wake up early, then I apply some Vicks Vapor Rub underneath my eyes. The vapors come into my eyes, forcing me to close them. Or, just lay in your bed, close your eyes and stay still. Even if you get itches or something, ignore them! Lay in your bed and you will drift off to sleep in about 5-10 minutes.
Drink something warm and get extremely comfortable. Listen to music without words, (because you'll end up thinking or singing along with words) and keep the volume down low. Good luck, and next time, go to bed earlier or at least prepare yourself.