Surfacing issues in creating a variable thickness

Hi I am trying to create a surface model of a coke bottle and I am stuck on a method to generate a variable thickness where the body of the bottle narrows to form the neck of the bottle in order to stiffen this part of the bottle ready to form the threaded end...  hope that makes sense.  My attempt so far do not produce the seamles blend at in the real thing ...  no pun intended lol

SolidworksSurfacing