My father got into a hit-and-run a few years back. The other driver was drunk, tried to offer him cash on the scene, and ran when he wouldn't take it. My father remebered the license plate number, and the other car was found and impounded.
Even though it was a day or two later and he had slept off his hangover, he wasn't charged with the hit-and-run or dui when he turned himself in.
I am not saying you won't be charged with the hit and run if you turn yourself in, but you may not be. I would talk to a lawyer. It would be very bad for you if someone out there got your license plate number and they found you before you turn yourself in.