Couldn't you just provide a background for the html page (custom) to give you what you want?
1) "hide the overflow on x" ==> sym.$( "elementName" ).css( "overflow-x", "hidden" );
2) "extend the background color" ==> $( "body" ).css( "background-color", "yourColor" );
Looks like this scrollbar is a property of the div of the stage. To remove it you just need to apply a css rule to the div:
You'll have to use a drag or an animate feature to view the full animation (but this is what you had in your original composition).