Have your TA (or PVP) mark your booking as "No Upgrade".
This should guarantee that you have the cabin you want.
I'd still check online every once in a while to make sure the cabin is still yours! We were "upgraded" (not on Carnival) once when we had booked a specific cabin. We had to call our TA to get our cabin back!
Have a great cruise!
"A truly happy person is one who can enjoy the scenery on a detour."
Golden Princess 2009 Carnival Conquest 2010
Grand Princess 2010 Island Princess 2011
Grand Princess 2011 Carnival Magic 2012
Carnival Dream 2012 Island Princess 2013
Carnival Magic 2013 Carnival Legend 2014
Carnival Magic 2015 Coral Princess 2015