Visa help: Double stop in China. Connecting in CAN to PEK from Siem Reap

Hello, I will be traveling from Siem Reap, Cambodia through Beijing, China to my final destination in the United States (DFW). I was doing some reading on Chinese transit visas and wanted some clarification on how this might affect my travel path. Currently, I’m traveling from Siem Reap, Cambodia to Beijing, China through Guangzhou (Canton), China. I’ve read that I can only receive a 72-hour “Traveler without visa”, but I have to leave to the United States from the same airport I’m arriving at in CAN. Is this true? I’m essentially doing a double stop. Below is my itinerary. Any and all help would be greatly appreciated.

Tuesday August 16, 2016
Air Vendor: CHINASOUTHERN
From: SIEM REAP
Departs: 11:30 AM
To: GZ
Arrives: 03:00 PM
Class of Service: [ U ] ECONOMY CLASS
Operated By: CHINASOUTHERN
Flight Type: NON-STOP



Tuesday August 16, 2016
Air Vendor: CHINASOUTHERN
Flight Number: 3113
From: CAN
Departs: 05:00 PM
To: BEIJING/PEKING
Arrives: 08:15 PM
Operated By: CHINASOUTHERN
Flight Type: NON-STOP



Friday August 19, 2016
Air Vendor: UNITED
From: BEIJING/PEKING
Departs: 04:10 PM
To: CHICAGO-OHARE
Arrives: 04:15 PM on Aug 19 2016