Nadine M, did you book directly through Princess or with a travel agent? If you went through an agent the documents will go to the agency first, then they will check them and forward them to you.
I wouldn't worry; "mailed" to a big company isin't the same as "postmarked"; it just means the process was set in motion. I'd give it a few more days.
Be sure and let us know when they arrive--I want to do the "doc-dance" with you!