US to Shanghai to Hong Kong back to US

Yes, you are definitely qualified for 144 hour visa free transit in wider Shanghai area and you do not need any kind of visa.

I hope you have presented your itinerary in a detailed way because your flight to Shanghai is not allowed to have Hong Kong as an immediate point before Shanghai and also, you are not allowed to have any additional landing within mainland China after Shanghai and before Hong Kong.

If your itinerary is within the above mentioned frames, you should just board the plane and enjoy your journey.

Upon your landing in Shanghai the first thing that you will do is to approach 24/144 hour visa free transit counter where you will apply for a temporary entry permit by presenting your flight tickets and your accommodation booking confirmation for at least the first overnight. After a short check, you will proceed to the immigration and finally to enjoy your time in Shanghai and neighboring provinces on your own.