One of the holes in the extension bar where it bolts on to the sight track will be oval, giving a bit of side-to-side free play.
If you first line it up with the riser - hold it in front a bright surface, so there is a thin gap visible between the riser and the sight track, now move it slowly so the gap closes. When it's aligned, the gap will close all at once.
I've never had to do more than that to get it right - you can also check it by putting an arrow on the bow, and setting the sight pin directly over an arrow. Moving the pin up and down and check that it stays aligned with both the nock and the point.
If they're still going right, then it's you or your arrow/bow tune at fault.