There are a couple of possibilities:
1) You exported a 4:3 project out of Premiere and the Articulate stage is wider (e.g. 16:9)
2) You exported the right size project, but your PAR (Pixel aspect ratio) is wrong
To try to narrow it down, have a look at your flash file in Articulate: is it "squished" (thinner than it should be), or normal?
If it's squished, sounds like the PAR coming out of Premiere is wrong. If it's normal, sounds like your project setting in Premiere is wrong, or has footage that doesn't match your Articulate stage.