Help with a movieclip loading to wide please

Hi I have a container_ mc that is 560x320wide. I have a “About Us” button beside it with this code in my actionscript file:

_root.about_btn.onRelease = function()
_root.loader_mc._visible = true;


The about1.swf is a 560x320 wide swf movie with pictures and images in it. When I preview my main movie and load “about us” page the about1 swf is stretched out much wider than 560px. It is about 700px wide and goes off the page.

Any ideas why my swf file is too wide?