Can I extend 72 hour visa?

Hi i am traveling from the UK to Xiamen, i did not realise i needed a visa and my trip is for 1 week. I see you have a free 72 hour free transit but what can i do to extend it while i am out there for the duration of my trip?

Also my return flight is not to a third country but back to the UK. Can i fly somewhere else first and return to Xiamen for my UK flight? Please advise. Thank you Stuart