Hi Daniel,
A corner pin works by moving the corners of your clip to the corners of the surface, so there will always be a distortion unless your clip is already the correct aspect ratio. You need to do the cropping and pan-scan before the corner pin.
Which app are you using the data in? After Effects, FCP or something else? If you let me know I can give you some pointers on how to get the result you're looking for.
J-P
John-Paul Smith | CEO | Imagineer Systems
www.imagineersystems.com