It would probably make you feel better to check your price elsewhere- get in touch with an online Travel agent, like expedia.com or cruise.com and ask them for a quote-just get them to check the same date, number of passengers & category. You also should ask about a guaranty. We almost also book a guaranty & usually get bumped up a couple of cats. we're booked on the Ocean Princess & sail 3 weeks from today (YEEAAAHHHHH). We booked an F- Princess shows us in D617 at present, but we called the TA yesterday & she said we're 2nd in line to go to a D & 3rd in line to go to an E. Also, we initially booked with Princess, then Expedia.com gave us another $50 off that rate just to move our booking to them.
Have you received any other prices for the same cruise, cabin catagory etc?
If not, you may want to try out bargain finder here, its easy and it will give you something to compare to, but sounds like you got a very good price already.