China tourist from Canada with single entry visa

I have a round trip ticket toronto -shanghai and a roundtrip ticket shanghai-hong kong. I plan to fly into shanghai, enter china using my single entry and travel around China for 3 weeks. Then fly to HK for one week and return to Shanghai airport to catch my flight home to canada the same day (not leaving shanghai airport but catching my connecting flight the same day within 4 hours). Is this OK for the the free transit?