I'm working on a type specimen sheet as part of a course I'm doing, and the instructions say it has to be 8.5 x 11 inches, double magazine spread. Does this mean its 8.5 x 11 per page (so times two), or is 8.5 x 11 the whole magazine?
As the size you state is US letter, I would image this is the page size and the spread would, therefore, be 17 x 11. Double check with your school, but a magazine with a page size of 5.5 x 8.5 (US half letter) would be pretty small.
Without seeing full brief I'd be edging towards 2 pages at 8.5x11 but I'd double check as well. There is nothing wrong with confirming something you're not sure of and at the end of the day it saves time in the long run.