Why am I seeing off stage when I test movie?

There are different scalemodes, and the default one is ShowAll, which will reveal things off stage if the window is wide enough. Either present the SWF in a window that you control the width of, or try setting the scalemode to something else. NoBorder for example will prevent the stars from appearing, but as you make the window super wide, the top and bottom of the stage will become cropped.

This is the script to add to frame 1:

stage.scaleMode = "noBorder";