I have played around with this I I think I got the surface results you were looking for. I am using SW 2012 so I had to use the STEP file and I only got an imported surface and solid. I recreated the three sketches from your picture the best I could. I tired to use both the filled and boundary surface commands with different sketches but in the end I got the best results using the 'Lofted Surface' command. Here is what I did:
Here I changed the transparency of the solid body so we can see the two bodies better.
From the picture you provided, it appears your sketches were made from the surface so I hid the solid for this tutorial just to get it out of the way.
I started a new 3D sketch...
and used the 'Convert Entities' command and selected the following edges.
Exit this sketch.
I created a second 3D sketch and again used the convert entities but made sure my end points of this sketch were coincident with my first sketch.
On the right plane I create a sketch with a spine making sure the ends of the spline was coincident with the two 3D sketches.
Using the 'Lofted Surface' command...
I chose the two 3D sketches as the profiles and the spline on the right plane as the guide curve.
here is the resulting surface.