I've attached here a version where I've done that next cleanup step, is this the result you were trying to make? :



The cleanup steps are:

1. Select the inside edge with the self-crossing loops in it.

2. Duplicate it as a separate curve object by running Copy / Paste (Ctrl+C/Ctrl+V). You can now delete the sweep surface since you won't need it anymore.

3. Select the inside curve and then run Edit > Trim. At the prompt to select cutting objects, just push "Done" or right-click in a viewport to indicate that the curve will cut against itself at self-intersection locations. Select the excess areas (using window selection from left to right that only captures things entirely in the window is useful for this), and then push "Done" or right-click in the viewport to finish the Trim and then it's done.

- Michael

Edit: Said the wrong way (right to left instead of left to right) originally.