Place the clip on a track in vegas. click on the "pan/crop" icon that appears on the left end of the clip. change the Rotation angle value (at the left) to 90 or 270 depending on which way your camera was tilted. That should do it.

Now drag the corner of the dotted outling of the frame (with the F in the middle) unti the clip fits in the frame (you will have black bars on the sides). Alternatively, you can zoom in untill you fill the frame by cropping out the top and/or bottom.