For the record, you would never want a transparent gemstone that had been faceted so shallowly.  When the facet angles in the pavilion (the bottom) are below the mineral's critical angle light just passes right through, leading to a "window" or "fisheye."  Diamonds in particular are cut to pretty specific proportions to be sure that they have good light return.  I'd recommend taking a look at some photos of faceted stones to get a better idea of their proportions--what you have is neat but not quite accurate.