The central square is smaller than any on the lap. That could have something to do with the hill. And as Don H mentions it centered on the lap.
Even with all that the 4/5 D stroke the hill should have gotten smaller or gone away.
The narrow W added some correction but not all the way to the edge, there is still some turn up in the outer zone.
The reason equal size squares on the lap are desired is because larger squares resist being pressed down during work more than small squares and they have more surface area to work the mirror. Pressure is higher and area more, more wear on the mirror. The squares are far from uniform size.
I think what has happened is the narrow W that was to put correction in the outer zone, because it was near COC allowed the differences of facet size to generate the zones, making those zones faster than the big W can remove them.
I recommend you redo the lap. I think it will cause trouble. You might be able to force the mirror into shape using strokes to concentrate work on the high zones, or pressing parts of the lap out of contact (stars or rings), or accented pressure (usually TOT). But that rarely results in as smooth a mirror as can be had if the lap is in good shape.
If you want to try to force the curve to better shape, here are some possible methods.
These large overhang strokes for working the center should work fast. I'd only do 1 turn of the mirror and see what happens. Would like the hill to come down smoothly, but if there is a little roughness there is time to smooth it as normal parabolizng strokes are used to get to the parabola.
It's the far off center part that works the mirror's center. Take that sideways stoke at the ends of the W out close to the edge of the lap.
This one leaves out all of the strokes except the far off center ones on one side. Red W is from 2/3 D out to the edge and magenta is from edge back into 2/3 D
For the narrow turn up at the edge, this accented pressure stroke will shorten the ROC of the zone just inside the turned up edge zone, so turn up is relatively less. Pressure with right hand, left hand no pressure only helps guide the strokes. For the 8" about 2 or 3 pounds should work. Don't do to much of this one either until you see how accented pressure works for you. The mirror is offset 1/2" to the right to starting position for the stroke. The W is stroked to the right across a zone about 1" wide. In the illustrations the yellow edge of the lap traces the stroking zigzag on the mirror surface.
Another thing might be to do a long narrow W like the one before except only 1/8 D wide. This could add correction in the outer 1/2" But it could also increase the zoning.
A better lap would be best but maybe you would like to try one or two of these first.
You already know what sort of lap I like.