Filling this 3D sketch

Hello, I'm trying to redo this 3d surface to have the inner loop edges flat.
I tried to create a 3d sketch from the surface edge, but I'm unable to get all inner point of the inner loop at the same Y position without deforming the spline in other axis.

Thanks for your help.

1 Answer

In 3D sketch use convert entities.

Start a 3D Sketch - select the Edge - click on convert Entites.

Repeat the same for other edges.

Use splice for the open edge and give tanget relation to it.

Here it is.