I am wondering if my situation will be ok for the 72 hour transit visa in Beijing.

I'm looking at booking a ticket from Seoul to Beijing (60hrs), Beijing to Phuket (5 days) and a return flight to Seoul that has a 2 hour layover in Chengdu (so Phuket—Chengdu for 2 hours—Seoul). I want to apply for the 72 hour free transit for Beijing, but I want to make sure my short layover on the way back in Chengdu doesn’t mess up the visa and the layover won't be an issue. Can anyone help me out?