Joining patch surface to other surfaces

I am trying to join these surfaces together so they can form a closed solid.
the intent is to model complex curved surfaces for CNC.
Can anyone tell me where I am going wrong
The patch will not seem to join with any surrounding surface.
here is the file
guitar.3dmodel.lesPaul.neck.3dm (803.4 KB)

Hi Chris - here are a couple of alternate methods of creating that surface.

GuitarHeel.3dm (404.2 KB)