I have been pretty successful with machine sewn bindings and have a few pictures to share that might help. First I cut my binding 2 1/4 inches and press in half with lots of starch. Wetting with starch before I fold helps the fabric stick to it self before pressing and I can get a good press and a stiff binding. After attaching the binding to the back, then fold the binding to the front and place the edge right on the stitching line. I then use my "stitch in the ditch" foot and move my needle from the center position to the right slightly. That way when I run the guide on the stitching line, it catches both the front and the back of the binding equal distance from the edge. The following pictures show how I turn the corner. Hope this helps.
I do not pin as I sew the sides, just use fingers to hold the binding on top of the stitch line
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When approaching the corner, use a stilletto to hold the corner down and take your stitching to the fold, then stop with needle down
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After turning and taking a couple stitches, remove the pin and continue to the next corner
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When completed, the visible stitch line should be equal from the edge on both sides
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After sewing binding to back, fold to front and pin each corner on the stitch line to hold in place
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