If I were you, I'd get that reservation made as soon as possible to lock in a rate for that date (especially since you already know when you want to go). Rates are very likely to increase over time and it's not very predictable as to when they will start increasing for your dates. June is a pricier time (in comparison to many other months) and they know people will pay higher no matter what.
For instance, I've been tracking the prices for a 7-day in March 2005 ever since the prices came out. This cruise is over a year away yet and it has already increased in most categories by at least 5%.