AM I eligible for the 72 hours visa?

Hi,
I m a student in shanghai (I have the X2 - one entry) since 2 months and in 1/2 month I will leave china to go back in italy (i already have the ticket to go back on7th august).
Before leaving, I am planning to travel to the South reaching Vietnam. My plan is to fly back from Vietnam on 4th or 5th August, to ask for a 72 hours free transit and then on 7th August to fly back in Italy. Can I do that?
Thanks a lot in advance