Now measure 1 1/4" from the fold, and cut to that length.
Now the ends should look like this:
Open up the ends, and lay them out as shown here. Position the right side piece on top of the left side piece, matching corner "A" to corner "B".
Pin together, and sew on the diagonal (shown in red). You may have to squish up the quilt a bit at this point to get the part you're going to sew to lay flat in the sewing machine.
Trim off the triangle, leaving a 1/4 seam.
Press the seam open. I run my fingernail along the seam, or you can use your iron.
Now you should be able to lay the quilt flat again, and it should look like this. A nearly invisible diagonal seam, that looks just like all the others. Take this back to your sewing machine, and finish up the rest of the binding.
Starting in the middle of one side of the quilt, you are going to wrap the binding around to the front side, placing the edge of the binding just to the left of the line of stitching you just made.
Holding down a small section at a time with your hand, sew very closely to the edge of the binding. If you take your time and use matching thread, this will come out very nicely.
Continue down the side of the quilt until you get about 3" away from the corner. Leave the needle down, and trim off the tiny triangle shown here.
Here it is trimmed. Be careful to only trim the tiny point that is to the right of the stitching line. This will eliminate some bulk at the corner. If you trim too much, you will be left with a hole in your binding. It's just that tiny corner- it will be about a 1/4" size piece getting cut off.
Now, with your needle still down, position the binding past the corner, and then hold in place the binding above the corner. It should form a nice miter.
And here is a view of the back. Your top stitching should be just past the edge of the binding on the back side of the quilt. Again, with matching thread, this is going to blend in well, and not be very noticeable at all.
A view of both sides of the completed binding.
Yeah, you're done!