There are a number of ways you can address this but you would need to provide more info on what is the source (eg Digital TV), how it is connected (eg HDMI), what the resolutions in (eg 1920x1080) and if you TV is set to "FULL / Pixel to Pixel" etc. Changes are however that the "Crop Edges" function in the TV Setup area that may fix your problem as it zooms the TV picture out slightly removing the overscan lines you are seeing. You can also set MC12 to "Crop Edges" on the Video Playback area if you also see rough edges when playing Videos etc.
Thanks
Nathan