Hi David, so right now your bottom curve is like this:



You can fix it by turning on control points, then selecting just 2 corner points at a time and using Transform > Align to make them vertically or horizontally aligned with the center point. In the align command pick the alignment point to be that middle point. You'll do the align command 4 separate times, 2 times to do a horizontal alignment and 2 times to do a vertical alignment on different pairs of corners so that they are all lined up like this:



Then you'll make a smooth single surface network once your input curves are smooth as well.

See the attached 3DM file for an example of the edited curves.

- Michael