Sad to hear that WebGL gave you a hard time. We got hit by random scaling issues too, and couldn't find any recent answers to the problem, but I've red somewhere that the website's css can be overriding your canvas settings.
Viewing post in Spirit Fire jam comments
Near the end of the jam I actually found what was causing the bug, the source was how I programmed by WebGL shaders and not the CSS. Essentially I had a 100x20 image rendered on a 100x100 object. Although the image width and object width were the same, the heights were different. This caused my image which was shorter than my object to be stretched by along the y axis by 5 times to fill the object. Thus I had elongated sprites.