Offset the last plane you have shown on the right so that it just hits the tip of the "bubble", then create a sketch with a single point at the tip. Start a surface loft using the end profile, and the new point. Set both profiles to "Normal to profile" and adjust the tangent lengths to suit.
Note: You MUST create the point on a plane that is normal to the plane running the length of your part. If you don't use a normal plane, your loft will not come out correctly.
Cheers patrick worked perfectly
Another great resource for the shape you are attempting is at DiMonte Group. The presentations that they offer are packed full of information.
some good stuff here,
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