Restricting Interpolation to 2D versus trying to lofting to next Z level contour

I have and outside and inside curve, which has lines connecting points between the outer and inner,

These lines are subdivided by 1mm, pending on the contour, they could be anywhere from 3mm to 10mm. I’m trying to interpolate these subdivision points. I have it working for the most part. How do I limit the interpolation to XY versus trying to continue to the next set higher up. Periodic is set to True