I have not stitched on canvas with mine, so I can't tell you what to set it on, but have you checked to make sure your bobbin is in correctly? Once I made sure it was and the tension is good on it, I would take a piece of scrap canvas and keep adjusting the tension on the top thread just a little at a time until I got it the way I wanted it. Is your bobbin thread too straight, crooked or how is it not looking nice?