Are the directions for cutting out squares/rectangles of fabric or is it an actual pattern? If it is the former (squares/rectangles) - then I would add the extra inches to the length and width (so if you actually want it to be 15 x 15 - then you would add 7 inches one way and 5 inches the other). I have made some easy totes and that is what I have done. Mine was a simple pattern cutting out rectangles of fabric for the outside and for the lining.