We should be fine, right....!

Yes, you are definitely eligible for 144 hour visa free transit in Shanghai area and you don't need any kind of visa.

You should just take care that your planned itinerary does not have any additional stops within mainland China. Of course, you are allowed to explore quite vast area comprising of Shanghai City and Jiangsu and Zhejiang provinces. The mentioned area has almost 50% of all US population :)

You should print out your flight tickets and have those printouts with you. Also, you will declare at check-in in Seattle that you will travel to Tokyo via Shanghai using 144 hour visa free transit. After a short inspection of your tickets, you will be allowed to board the plane.

Upon your arrival in Shanghai, you will approach 144 hour visa free transit and fill out the blue form. Shortly after, you will get a sticker in your passport and be allowed to exit the airport. You are also advised to book for at lest the first overnight your accommodation in Shanghai because during the filling out of the blue form you will encounter a couple of question regarding your accommodation.