not to rain on your parade or the affirmation everyone else is giving you, but isn't 24cm REALLY small for an 11.5 size boot? i have a size 9 boot, and my board's width is 25.2cm. with the bindings attached at 15 / -15 duck, i still have slight overhang.
basic snowboard sizing charts on most retail sites suggest 24cm and less to fit size 8 and down, 24-26cm for 8.5 to 10.5, and 26+cm for 10.5+. of course, this is all a matter of personal preference, but a 24cm waist to an 11.5 boot seems a little extreme.
hope you get your situation resolved. it'd be a shame to not be able to use such a pricey board.
i love my life