If you interlock your triangle cuts, you'll get a lot more per wof, and that will cut down a lot on waste and yardage needed. The way you have it figured, you'll have 40-50% waste, that would not be acceptable to me.
I'm not sure how you came up with 2.5x3.5 rectagles, seems to me that you can get two out of a 3.5*3 rectangle.