First, your composition has been made in Edge 2014 version. You can upgrade to the latest version which is 2014.1.1.
Second, you can try setting the "Center Stage" to "Both" for the Stage.
Hello and thank you for responding,
I actually had big problems when I wanted to go from the 2014 version of the 2014.1 release, many "exception error" so as I am at the end of my project I do not want to risk create more problems.
For the "center stage", I have already tried and instead create a space below it distributes the top and bottom space always with a scroll.
The version 2014.1.1 has been released specially to fix such exception errors and so many other bugs as well. I would recommend you to try it.
Now coming to the issue, if you don't want the blank space to show up, then two things can happen:
1. The stage and its element won't scale proportionally, which will be very bad, so Edge doesn't allow that option.
2. You can set the "Center Stage" to both and "Responsive Scaling" to "Height" so that whole height of the browser window is filled with stage animation, but then it will introduce the horizontal scrollbar, to avoid disproportionate scaling of the elements when you resize window.