Having trouble scaling strokes in After Effects

I am new to after effects and I am having trouble understanding scaling shapes in After Effects. I have an initial shape ( image 1 ) that I wish to expand and animate to a wider shape ( image 2 ). But as you can see, the gray stoke also widens when I expand it when I want it to remain the same stroke width as the previous image and just have the shape widen. Basically I want image 1 to animate to a wider shape and look just like image 3 without the stoke becoming thicker. Hope that makes sense.

Images are here: http://ift.tt/1ChWXHj

Any help will be most appreciated.