Already in country with single visa but want to see another Asian country before I leave

Hello, I am an American citizen. I am a medical student here in China for an internship at a hospital. I was only allowed a single entry visa to get here. I have one week left in China and I will be done with the hospital. I want to fly to Thailand or South Korea then return to China (Shanghai) to visit Disney one day then fly back to America the next day. I already bought my Disney ticket for May 30 and my flight leaves Shanghai to US on May 31st. Is it possible to fly to another country during May 26-29 then apply for a 72 hour or 144 hour free transit when I return to China? Thanks for your help.