Am i ok for the 144 hour transit pass?? Please help me

Hi im looking at travelling london to shanghai (use the 144 hour visit) then fly shanghai to vietnam for 4 days, get a bus to cambodia stay there for 4 more days and then fly back to the london but the flight is cambodia-shanghai (7 hour layover) then shanghai to london, im really worried about this due to the fact that they will be able to see im returning back to shanghai on my return flight to the uk.

can somebody clear my mind as to if this is ok please?