How about finish the construction then draw an arc that would trim the whole shape? It looks like you are creating a corner then you're going to build off that?
If you are just trying to lathe that corner, you have the problem that the shape needs to be perpendicular to the first segment in the path. Always a problem with arc paths. If you wish to use follow me, lathe the arc shape about the center of a circle, then isolate a quarter of the dome for your corner.
[edit] Oops. See Jean's notes about hidden geometry below if you are new to that. Very helpful. Otherwise you can't do what I am proposing.