AlvaStitcher

I am using my DSM to sew some covers for tools and gears for an airplane that my son is helping to restore. The material is duck and I am having a real problem getting the tension correct. There are three layers of fabric and the upper thread is looping through to the back and the bobbin thread is laying flat on the fabric. I have adjusted the upper thread tension all the way from 3 to 9 but the problem still exists. Do I need a commercial upholstery machine to make these? I am using a #69 weight nylon thread with a jeans needle in the machine. Need help before I throw the whole project out the window! LOL
This picture shows the top of stitching on wrong side of fabric
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This picture shows the wrong side (bobbin side of fabric) which will be the upper side when project finished. Hope this makes sense.
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Thanks for your suggestions.