Ideally binding is supposed to be the same in the front and back of the quilt if it is 1/4 inch or other. I would use the seam allowance that enables you to do that. You might want to cut a little section at 2-1/2 of scrap fabric and try out some seam allowances first. Judges also look to see that you have hand sewn the little 45 * angles on each corner of the binding closed.