Is this covered by a 72 hours free transit?

Hi,
French passport, traveling in China for about 15 days with a valid visa. I'll "leave" mainland to go to Hong Kong. But my flight to leave Asia is from Shanghai. So my question is: can i take a flight from HK to Shanghai and, on the same day, from Shanghai to the US? Would it be okay to re-enterfor few hours (I wont leave the airport but ill have to pass the immigration to check in again).
Thank you very much for your help!!