Flight plan change

Hi! I'm an Italian citizen in China. I was given a single entry visa and I leave on August 12th.
A friend of mine who lives in Singapore invited me so I'd like to go there.
I know I can't enter china again so on the way back from Singapore I would land in Guangzhou at 10am on August 12th and from there I'd take the flight to Rome at 22:40.
So I'd have to take my luggages and check in for the flight to Italy without leaving the airport. I'd still have to go through customs though because it wouldn't be a transit but a different flight.
The chinese embassy in Italy doesn't know anything about what you wrote here.
What should I do? Just show them my ticket when I get to Guangzhou?
I would be fine with staying in the airport for 12hrs as long as I can go to Singapore.
Thanks in advance