Ok, I need you to clarify what you did and what you're now trying to do..
- When you say you "mixed with all the master fx off" do you mean the Master Echo/Master Reverb, or any/all plug-ins (EQ/comp/etc) in the plug-in slots in the Master tab in the Smart Controls pane?
- Why are you now returning to that song? Are you looking to master it with EQ/comp applied to the finished mix? If so, then don't return to the original project file, create a new project, and drag in just the finished mix audiofile, which should show up as one stereo track. Then you could apply mastering processing to either the channel itself, or to the Master track.
- If you're saying that when you "open the mix file in the new project" it opens to the original project layout (multiple individual tracks), then you apparently didn't actually bounce it down to an audiofileâ€”I'd guess you must have shared it as a project. To bounce down to a finished (stereo) audiofile, use the Share menu option called "Export Song to Disk..." and select WAVE > Uncompressed 24-bitâ€”this will create the finished full-quality stereo audiofile on your hard disk, which you can play in iTunes, QuickTime Player, or any audio application, and which you should be able to drag into a new project (onto a single stereo track), as with any audiofile.