Problem using Photoshop CC Content Aware Scale

I am sure there is a screw-up in my thinking because I know Photoshop is always right. 🙂 I am trying to use Content aware scale to stretch a background. I am preserving the lamppost using an alpha channel. I have incresed the size of my canvas. No matter what I do I can't get the handles to just pull out left to right or vice versa. When I pull out to the right in also increases the height of the image which I don't want. I would appreciate any help I can get. I'm up against a deadline and just can't figure it out. Thanks in advance for your help.