Bobbin Winding
If you stitches are not sewing correctly, check that the cotton on the bobbin is not loose. When I wind my cotton on to the bobbin I place my index and thumb over the cotton to hold it firm, so that when it winds onto the bobbin it is not loose. The cotton must be firm. If the cotton is loose, your stitching will be loose and may develop loops underneath or on top.
Happy sewing
Judith aka genie