Sorry to burst your bubble, but you did book a 6a GUARANTEE !!! That means you're guaranteed category 6a with a possibility of an upgrade... the chances of getting an upgrade is good, but if there are still some cabins in that category by the time your cabin gets to be assigned, then that's what you'll get. Also it can be anywhere on the deck, in front, in the back, close to stairs and elevators where the noise is louder, etc... I don't like to book that category, since you can have any cabin available. And I surely don't wanna be stuck with one of the first cabins foward or one of the last cabins aft. Those are the worst !
It's really too bad you didn't get your upgrade... I guess you lucked out there.... but like Steph_texas said, try to get a better upgrade by calling Carnival... it can't hurt, and you might be able to get something better... and since you'll be on your honeymoon... who knows !!!
If I guessed correctly, you'll be on a Conquest class ship, or a Destiny class ship... which means you have a cabin way in the back... definitely try to call CArnival and get another cabin... you'll hear and feel the motors a lot... it really shakes in the back, and can be very very noisy...
Anyway, I really hope you get a better cabin... but even if you don't , don't let that ruin your honeymoon... I'm certain you'll have a great time !!! And most importantly, enjoy your cruise !