OK, here is what I do....
leave about 8 inches loose before you start stitching the binding on and stop within about 8 inches from where the ends will overlap...
Then, overlap the ends the same amount as the original width you cut the binding..and cut.
ex. if you cut your binding 2 inches wide and folded it in half, then over lap the ends by 2 inches.
Then align the ends at a right angle to each other with right sides together so that you can sew a diagonal seam across the ends.
Finger press the seam open and straighten out. It should lay exactly in place. If it does, you can go back and trim the seam to 1/4 inch and finish stitching down the binding.
As many times as I have done this, it always comes out right, but I always check it before trimming.. Dont you know that the one time I trim before checking it will be wrong..lol. So, I dont take the chance...
Hope this helps..