Okay - so as Early Saver you can claim it until the day before the ship sails. Believe it or not, not everyone books into the "Early Saver" program although I think it is a good idea. Other cruise lines (RCL and NCL have dropped the program and price guarantees).
If you already paid in full then any price differences will be given to you in onboard credit - that is how it works.
Most people wait to pay in full for the day it is due - usually 90 days out before the cruise. But no harm in what you did.
Mike is right - all the cruise lines now have a "flat pricing" rule where no one will advertise a lower price than Carnival's - or vice-versa. It "should be" the same price no matter where you go.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.