You did everything correctly. What you are seeing is the fact that from the middle of the screen you are looking at the panel off to the right from an angle. So the distortion that you perceive is just the angle of motion as the panel rotates into view. This is a perspective that Vegas gives objects that are to centered.
Notice that when you look at the 3D view from the top and position the panel exactly 90 degrees perpendicular with the screen in the top view, which should make it invisible, it is already visible in the perspective view. If you move the track position to the middle, it disappears from view at a 90 degree angle as you would expect.
The only way to correct for this is to use a Nested project. Create a separate project to rotate from the middle of the screen and then drop that project into your main project and position it to the right, it would do what you want.
In this separate project, the Track Motion would Position the frame at X: -960 to move the pivot edge of the frame to the center of the screen. Then change the Rotation on the Y: from -90 to 0. This will make the panel rotate exactly in the center of the screen like a door. Finally, drop this project into your other project and move it to the right where you want it.
It will look the way you want because the perspective will be from the front and not from an angle off to the side.
~jr
http://www.johnrofrano.com
http://www.vasstsoftware.com