Experiment with applying an A/R (aspect ratio) effect to the clip or clips. Or try similar export A/R choices. Crop and Zoom may do what you want.
To see exactly what you're working with, please share the project. Then someone can offer specifics.
Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
If it contains sensitive material you can link it in a personal message (PM) to me, via the envelope above. Be sure to FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to share it.