Hi Cube,
I have looked at your file and see that you are blending in sections.
If you run the Rebuild command on you profiles and set the tolerance to 0.001
you will be able to blend as one surface.
If you look at the photo attached you will see I have added another model (right view top model)
where I have adjusted the top curve as it was to close to the extruded outer profile at
the one end and when blended was causing a small bulge.
Hope this helps.
Barry.