You chose an anamorphic format that should have a check box allowing you to toggle anamorphic on or off, you want it off.
However, you seem to be looking at proxies in the wrong way... You’d probably be far better off using a codec with the same pixel dimensions as your camera original, simply choosing a less demanding resolution and codec. That way, all of your graphics and text will translate appropriately when and if you ever wish to reconfirm using your camera original.
David Roth Weiss
Director/Editor/Colorist & Workflow Consultant
David Weiss Productions
David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro Legacy forum.