Do I qualify for the visa waiver 144 on Royal Caribbean cruise from Shanghai

I am arriving in shanghai for 1 night , then pick up cruise to Japan 7 nights, back to Shanghai 2 nights on to Singapore then Australia, I understand I qualify for the 144 twov waver, I am cruising with Royal Caribbean also and am worried they won't let us on the ship with just the 144 twov, Ive called them & they weren't much help, did you just show the stamp in your passport when you got on the ship? was it easy to apply on way back from the ship for the 144?

Thank you in advance,Caroline