How to import still of video into pixelmator

How do I import a still from a video clip frame into pixelmator and save its aspect ratio? I can't seem to go straight from FCP 6 to pixelmator with this process and iPhoto doesn't allow me to import from FCP either. I have been exporting it from FCP to dropbox and then to pixela

mayor but when the image gets to dropbox the aspect ratio is wrong and the image looks stretched vertically. Nothing i seem to do in pixelmator seems to work. The video was shot with an XL2 in SD. Here are the clip properties

Rate 29.97

frame size 720 x 480

pixel aspect NTSC-CCIR 601

anamorphic is checked

I have tried changing the AR in pielmator but nothing i do puts the image back to its original size. I am trying to do an overlay with the same clip with one that i took out an extension cord out of the background on. Any help would be greatly appreciated.

Thanks