Prices for Feb/March next year are currently £2998 for a couple in the cheapest inside cabin, so you did well with your price. I guess last minute prices may fall, but that is always a calculated risk.
Personally, we would rather stay at home than have an inside cabin, and we will only fly if we can have PE seats, so the budget lead in prices are of no interest to us at all.
We have paid well over twice the price you did for our forthcoming Britannia Caribbean cruise in December, and believe it is money well spent, and better value for money than having an inside cabin and a cramped flight.