How to scale with perfect shape?

I have take a rectangle and rounded the corners. Then i added a hairline with thickness. When i stretch the rectangle the hairline get distorted. (As shown in the above video)

I tried to fix the issue going in the outline option stretch to 100 and it works but later when i tried to add countor. As i noticed that the top and bottom match but the right and left not match with the top and bottom thickness. Any suggestion or help how to fix. Thanks