hi I noticed from your renders that you have not combined the two halves.
without combining you will always have a little bit of a seam. the first thing you have to do is select one half and shift select the other half ,then under the polygon tab click on combine to make the whole thing one mesh.After this you will have to merge the vertices in the center where the two halves join.
Finally you need to select the center vertices once again and go to edit polygons and at the bottom select normals and choose the soften/harden option, click on the preferences box and select All Soft...it will be set and 180 and then apply.
this will smooth the join.
If though before you have joined your mesh together the center egdes come to a ridge you will still have this ridge although it will be softer , you will have to tweak the verts to level the join to your liking.
hope this helps..goodluck.