Thanks for helping. The easiest way is probably if you open the HelloWorld index.html, run it, then observe the behavior as you make the window bigger/smaller. It scales properly.
Then just wrap the canvas and script call in a simple empty div, no ID or class even needed. I've attached to make it simple, plus a screen shot.
Run this, then observe that it scales down, but not back up. My image attached shows the Cocos2dGameContainer with a margin 0px 278px. That second number grows as you scale up. Thus proving that space given back by the window is being taken by the left and right margins and not given back to the game size.
The inconsistency of scaling down but not up to me is the part that shows something's not right.
Let me know if I'm missing something or if there's a real issue here.