Well, based on the two accurately-sized Cobrahead Phasers I have, the dimensions are:
Season 4 Type-II (Larger)
Length: 208mm, from end of handle to emitter tip
Width: 57mm, widest point at Power Level Indicator
Height: 45mm, highest point just in front of thumb pad
Season 5 TNG Type-II (Smaller)
Length: 197mm, from end of handle to emitter tip
Width: 55mm, widest point with no Power Level Indicator
Height: 42mm, highest point just in front of thumb pad
The handle width is 36mm for the Season 5 version, and 35mm for the Season 7.
All around, even based on the smallest of the screen-used Cobraheads, it would appear that your 3D model's a little bit on the smaller side in terms of length and width.