After Effects Export Problem!

Hi,
I have created a animtion in Flash 1920 x 1080 .MOV file, then done some editing in Premiere and exported that also 1920 x 1080 but with a H.264 codec... I then put that into After Effects on a new composition that is also 1920 x 1080 but the video appears on the canvas mis-sized, I have corrected that by pressing fit to canvas and all looks ok.

I then did the work with the camera, also looks fine, then I go to export, choose the H.264 with everything else the same (Or so I think) as in Premiere but it says settings mismatch will be resized to 1920 x 1080 (The same size I know?!?!)... So go ahead anyway and once I render the file has white lines at top and bottom along with some black ones... Does anyone know what I'm doing wrong?

Driving me crazy!

Rich