Like Deege says- Don't worry about it. I always do the "guaranteed cabin" thing. You book the category you want- Oceanview, interior, balcony etc and they "guarantee" you at least that category of cabin. So far I have always been upgraded. Not nessacarily to the best upgrade, but at minimum you get the one you requested. (I.E. We booked an interior on our Alaska cruise and got an obstructed Oceanview for the same price) I booked through a Carnival booking agent and he was nice enough to tell me what we were given (of course he made the disclaimer that it COULD change). Since you booked through Expedia, your only choice is to try the trick peachcrek mentions, but be aware that they don't tend to assign gaurantee cabins until a couple of months before the cruise..
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013