How to stop zoomed clip from stretching?

[ralphhelp]

Every time I use the zoom effect on a clip, it stretches the video clip to make it fit. (So it won't have the black bars I guess.) However, it looks really weird and I don't mind having the black bars anyway. I can't seem to turn it off though and I cannot find any info online. I keep messing with the aspect ratio but it doesn't seem to be doing anything.

 

I would really appreciate any help. Thanks!