You need to consult immediately with local counsel BEFORE you go to the police and make any kind of statement. You may face charges other than DUI under these circumstances.
The longer you wait, the worse things could become. Call someone tomorrow!
Best of luck.
I agree with Attorney Buckley's answer and would add that you probably can not be charged with a DUI under these facts (your original question), but should contact a defense attorney immediately, before you might be placed under arrest for hit and run.
Consider Ed Blum, he is a poster on AVVO, has a profile up and is an attorney in your area that handles these.
Good luck with your situation.
You absolutly need to consult with a DUI attorney prior to contacting the police. They can charge you with a DUI and they may be able to circumstantially prove it. Having said that, however, it may be much more difficult to prove unless they have you at or near the time of the collision. You need to consult with an attorney who can best advise you in order to minimize your "exposure".