Yep, you're good. If you do online check-in, you basically just get a booklet that is all general info with your baggage tags. (The only difference if you didn't do online check-in is that there would have been a couple of pages that you needed to fill out.)
It's not like a plane where you need to print out a boarding card. You will check in for the cruise -- give them the signed pages that you printed out; show them your Birth certificates and driver's licences and they'll give you your KTTW card -- that's your boarding card!