Transit Flight

hello,
I am an italian exchange student in Shanghai. My visa is an X2 (with only one entry and one exit).
My flight back from shanghai to Italy is on the 1st of july. Before coming back to italy i would like to visit seul and Japan. as i cannot extend my visa anymore (already extended with one more entry for going to Hong Kong) they told me that the only way to visit South Korean and Japan and not to loose my flight back from Shanghai is going to South Korea, then directly to Japan and coming back to Shanghai not more than 144 hours far from my flight back so that they can consider shanghai as a transit. Could you confirm it please cause I have only a doubt: for a transit I should not pass twice in the same place (for example Milan-Shanghai-Milan is not a transit), as my flight trip should be SHANGHAI-Seul-Tokyo and then Osaka-SHANGHAI-Milan (So complicated I know..) will I have any problems for the transit in Shanghai?
Just for information i am going to spend 2 weeks in total in South Korea and Japan.
Thank you in advance
Luca Bozzini