I understand that you are having some issues with the SlingPlayer signal since it does not fit in your TV screen in a proper way.
Most of the times, this issue is related to the cables in use and the resolution of the set top box. The following thread will provide you with some instructions to follow in order to fix this issue.
I had this problem too.
I checked here on the Slingbox forum and found this post/thread.
I checked my cable box settings, mucked around with a few settings, but to no avail.
Finally, I looked at the the Slingbox website, while watching my Slingbox.
I found a "Zoom" button in the bottom right. I clicked on that twice, so that a "D" is displayed, and I got my full screen view!
There are actually several options on this Zoom button. Play with it until you get your desired view.