Hi Cali - Welcome to Cruise Mates.
My wife & I did the cruise you are taking last October and had a blast, despite a slight deviation due to a hurricane. In PV we took a sailboat ride in Banderas Bay and swam it it's beautiful waters and in Cabo did Sea Treking. What a treat. Be aware that you will have three sea days, we found this very enjoyable and Carnival will provided you plenty of diversions.
A slight modification to my friend Kat's comment above. The early check-in is actually at the Carnival terminal not at the Queen Mary herself.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014, 2016, Royal 2017
Star Clippers: Royal Clipper 2015