You can see looking at the nadir footprint that your lower rail needs adjusting to the left (when standing behind the camera).
It also appears you need move slightly backwards on the upper rail, as it looks to be compressing the circle slightly.
It is important to never allow control points to be placed on the panohead of tripod legs and just as important that control points never end up on anything that moves I.E: Shadows, People, Clouds, Trees, Branches, Cars, Buses, Boats etc.
After making these adjustments and following the guidelines, please tell me what your min/max/average control points read after optimizing.
I'm also not clear on the quality of the Panosaurus and it's limitations via flex and rotation flaws etc.