Hong Kong to Shanghai, 72-h-Visa for Shanghai, Shanghai to Frankfurt with 2-stopover in Hong Kong

Hello,

I am a German citizen doing a trip through Asia. Currently I am in HK and want to go for a short trip to Shanghai (on Sunday 26th of April) to visit the motorshow. I already have a plane ticket for the way back (Wednesday, 29th of April) from Shanghai to Frankfurt, Germany, via Hong Kong (2-h-stopover). Am I eligible for the 72-h despite my stopover in Hong Kong on my way back to Germany (of course I won't leave the transit-zone). I am a little confused... My alternative is getting an express via, but that is expensive and I need to go to SH via Shenzen.

Best
Stefan