There really isn't an official boarding pass anymore. You can ignore the app, bring ALL your paperwork to the port (passport, vaccine card, your travel summary) and just show up. They'll get you through the usual routine...no problem.
However, if you do the app stuff, you'll be on the ship faster with less hassle at the port. Do what you can, ignore the rest. OR you could use the web-based app. It will allow you to do almost everything that the phone app does (can't buy internet, add security photo, maybe a couple of other things). If you want to try that, go to the Personalizer online, click on your cruise, scroll down a little until you see the logos for "AppStore" & "GooglePlay". Right under that is the link for the web-based app. You use your Princess log in for user name & password.
Once you're on the ship, you can ignore the app and just use your Medallion to open the door and make purchases...just like the "old" cruise card.
They're trying to phase out the cards, they should be available, but one never knows.