Start with some scrap material first. Rethread the machine. Adjust your tensions, start with the upper, then the lower, sew a couple of inches each time you make a change. Write down what the tensions were set at. Eventually, you will get to a top one that looks good, then a bottom and then you can just combine the numbers you wrote down together for your perfect stitch .... until you change fabric, thread, needles or sometimes it seems all it takes is a sneeze to throw everything off again. Good Luck!
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