I'm no doctor but I've never heard of a borderline diagnosis. You either tested positive for the antigen or you didn't. Did you doc check for HEP B surface antigens and antibodies?
By the way, HEP B is one of those diseases that can be transmitted without us ever finding out how we got it. I've never used drugs or needles, have always practiced safe sex (and have had my partners tested), no tattoos, no blood transfusions. No idea where I picked up HEP B. My hepatologist thinks I may have gotten it as a child but we will never know for sure.
Hope you get good news and good luck!