Add a MeshSmooth modifier with 3 Iterations. On top of that add a Shell modifier with an Inner Amount of 1 and an Outer Amount of 0.
Moving onto the guitar heel. Create a new Box in the Front View with 5 length segments, 1 width segment and 7 height segments.
Convert the Box to an editable poly (or add an Edit Poly modifier) and move the vertices in the Front View to define the heel. The top two rows of polygons will also define the neck and headstock of the guitar.
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