Since you still have a couple weeks before sailing, you can have your TA check with the cruise line to see if your request can be changed to your preference. "Peachcrek" is right, though, in that your assigned dining room corresponds to your cabin location. Carnival has gone to the 4-seating-time system - interesting that they divided up the early & late seating times this way.
Be aware that your dining request is just that - a request - and there is no guarantee that they will assign you just what you ask for. But you can ask for changes to be made after you board. As Peachcrek mentioned, if you can't get it done before your first dinner, you can request a change right afterwards. Who knows? You may find you just love the other folks at your first assigned table and may not want to change!