I noticed that Sketch1 is not constrained, or making any use of symmetry about the origin.
There are also redundent workplanes.
I would suggest reading these documents
http://home.pct.edu/~jmather/content/DSG322/inventor_surface_tutorials.htm
particularly
http://home.pct.edu/~jmather/AU2006/MA13-3%20Mather.pdf
http://home.pct.edu/~jmather/AU2007/MA105-1L%20Mather.pdf
and the curvy stuff tutorials here
http://www.dimontegroup.com/Tutorials/
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