Hmmm. I have this problem when I'm finished a project, and all I do is save and play the SWF file. However, if I publish the movie as html, it constrains the proportions within an HTML document,so all you see is what's confined in the stage. However, doing this on the swf file itself, I have no idea how to do.

If you go to file>publish settings , and tweek those a little, that might help.

Export it to .swf via the File > Export menu and it should have the proper size.

I already do that Demos but I'll try what Ren said and see if that works.. as for now I have a totally cheesy solutution which is just putting a top layer that blocks out everything except for the stage.. pretty weak solution but I'll try the HTML thing right now..