I know this machine. Have you swapped over to the wide stitch finger? Unlike many others, there is no lever to retract the stitch finger on this machine, you have to physically remove them to swap the two sizes over to the appropriately sized one for the cutting width or leave them out completely for the narrow overlock/rolled hem. The manual really doesn't help too much in understanding how the cutting width, tension and stitch fingers work together to create the different widths.
I suspect your loopers may be set at too high a tension but it isn't obvious for your normal stitch because the stitch finger you're using creates a minimum width. When you move to the higher width, you have more fabric that is no longer supported by an appropriately wide stitch finger so the edges are being pulled in by the tension of the loopers.
I suggest:
-- change over your stitch fingers to the wide one, see page 25 of your manual for info on where they are stored and how to remove/swap them over.
-- reduce your looper tension to 3.5 and tweak them until you get a good wrap of the edge at the wider width that isn't so loose it extends beyond the edge of the fabric or unbalanced so it forces one side (upper or lower looper) to be pulled over to the other side.