If you discover an opening in a just-stitched seam, the problem has likely occurred because you have selected the wrong stitch for the project or the weak thread broke when pulled through the machine. To prevent this problem from repeating, use a high-quality sewing thread or use the correctly sized thread for your project. Also check the stitch balance and readjust according to the fabric and thread used.
Crooked or Wavy Seams
Stretchy fabrics are notoriously difficult to sew. Often seams look straight as they pass through the machine. However, upon closer inspection, seams do not lay flat at all, but look wavy. To avoid wavy seams, use the differential feed setting on your machine, setting it according to the fabric used. When sewing, apply minimum pressure on the presser foot.
Jammed Sewing Machine
A machine that stalls or jams during a project can frustrate even the most seasoned seamstress. Unthread your sewing machine and take out the bobbin. Discard any loose thread or lint from the bobbin case. Rethread your sewing machine. Insert and rethread the bobbin. Busy seamstresses should inspect their bobbin regularly. A nick along the edges may catch on thread as you sew, jamming the machine.