Is it in the overscan area? That's the area anywhere from a half inch or so all around the screen boundy. If so, it won't show on 99.99% of TV's. If you still want ot get rid of it and/or play off your computer you can resize.

Click on the pan/crop button (right edge of event) then in the window that opens click on the frist key frame, then right click on the image and select 'match output aspect' click the little "+" sign, click on last keyframe to be sure you're still OK, if not repeat steps. The image should zoom out and fill the preivew window to whatever your project size is. You'll need to repeat for each event or drop the finished project on the timline and just do it once. If or not that will effect quality depends on the file format you rendered too, assuming you have already.