As long as what you cut off of the sides doesn't need to encroach on the support you should be fine. I'm trying to remember residential sizes and think a king is 72" and a queen 60". Do you have 6" of overhang on each side? If so, it shouldn't be a problem.
While you're at it, could you send me the scraps so I can add them onto our bed? The wife and I still seem to fight over space even with 72"...