Let's get back to the lure for a minute, even though you cut your lure lip slot before you turn it down if your centers are not perfect then your cut will be off. Looking at the lure after turning, from the nose with lip in your hand may see that the lip is leaning to one side, just a little, that might cause the lure running to one side. One thing that I do after turning down the lure I place the lip in the lure and place it on a flat surface and see how true it is make sure the lip is all the way in, at this point you might see that the lure it not in a straight line, the whole lure might be just a little off, at that point you must shave a little off the lip bottom of the lure on the that side needs it to straighten the lure. One more point if you cut your own lip then the lip must be square on the bottom, if not shave or cut a new lip to make it right. I hope this makes sense sometimes easer to show than write about it.
Wayne