The centering can be adjusted, how to go about it depends on the machine. My 158 series machine is out on loan right now so I can't check it, but I did just have a 152 series machine pretty well apart, and on it there was a horizontal bar running from the needle bar over the gears for the ZZ and other pattern discs, and there was a set screw holding that horizontal bar in a clamp and I loosened it and then moved the needle to where I wanted it and then tightened it back up.
If you adjust it check the ZZ at it's widest setting and test turning by hand, to make sure the needle doesn't hit the plate on one side or the other. Adjusting the stitch width is likely controlled by a small cam near the mechanism holding a pattern disc, at least it was on the 152.