I think you will find that pretty much every remaining voyage on the QEII timetable is fully sold out with waiting lists for cancellations. There are an awful lot of people who are very fond of that ship and, as with Concorde's retirement as soon as the end of service was announced, if you didn't book instantly, you had no chance.
I also tried for the maiden voyage of Queen Victoria in December but that was all snapped up within hours of going on sale...