So it appears they arbitrarily moved you to the new 8 night transatlantic, without your input? You booked directly with Royal Caribbean? An agent would have headed this off before it happened.
You can cancel the booking or change it. It isn't an 'I hope they let us' thing. You still have over a year to do that before you'd get into the penalty phase. Just do not pay it in full as that is not due for a long time.