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I had a look at your .swf, and I believe your issue is related to the stage scale mode.
In Flash, when you test the movie it has the stage set to not scale.
But the default when loading a .swf in the Flash Player, or in a browser is to show all.
Try this line at the start of your document constructor (the start of your project, either in your document class or on frame1 or wherever you've put the code).
You may have to import StageScaleMode and StageAlign.
stage.scaleMode = StageScaleMode.NO_SCALE;
stage.align = StageAlign.TOP_LEFT;
Also, TOP_LEFT may not be the correct one, so try a different align if that doesn't work.
Or try leaving it out and just set the stageScaleMode.
Hope that helps.