Along with barny's suggestions, let me add one more. Does your machine currently zigzag all the way across on its widest setting? If not, you may need to oil what's called (I think) the bellows. If you open the door on the left and look beside the needlebar, you'll see a round thing that goes in and out when the needlebar moves from side to side. It may need oiling. If it doesn't move freely, it will prevent the needlebar from stitching the pattern.
Tate