You may be charged for hit and run, but it is a weak case since you stopped and had a conversation with the victim and since you stopped at a safe place and returned. As you probably know it would help you to find the witnesses. Perhaps a newspaper advertisement asking for anyone with information about the accident to contact you would lead to some witnesses. If you are convicted of hit and run and the person is seriously injured you could face jail time. You need an experienced criminal defense lawyer to represent you. If you cannot afford one the State of Washington will provide you with a public defender (or the county will).
However, you have many facts on your side: 1) minimal impact; 2) conversation with the victim; 3) the victim did not even drop his briefcase; 4) you stopped as quickly as you could; 5) you had no intent to hit and run and you must have intent in order to be guilty of a crime; and 6) the victim suffered minor injuries, if he suffered any injuries. I do not think this is a strong hit and run case from the state or county's point of view. That being said, you still need a good criminal defense lawyer. Good luck.
I hope that I have helped you and that I have answered all of your questions. Please contact me if I have not answered all of your questions. If my answer is satisfactory please accept it. I really appreciate positive feedback.
In the future, you can specifically request that I work with you on your legal question. If you have specifically requested that I answer this question, thank you.
Please be aware that my answer is not legal advice, it is merely information. You and I have not entered into an attorney/client relationship. The only way that I am legally responsible for your legal rights is if you have signed a written retainer agreement with my law firm.