From the Princess web site which has just been updated this week:
Complimentary Room Service
You can call for personal room service at any time of the day or night. To have continental breakfast delivered to your stateroom, just fill out the breakfast card included in your stateroom portfolio (one is also placed on your pillow) and hang it out at night on your stateroom door. For a full stateroom menu, please see your stateroom portfolio or call the number listed in your telephone directory.
Unless you ordered something not on the room service menu, you shouldn't have been charged.
Like Paul, I'd like to know how much you were charged and for what items.
I know I'll be very disappointed if they start charging extra for room service
. It's supposed to be included in your cruise fare.