Check your routing. The only way that the exported audio can be different from what you've been hearing is if the routing is different.
Make sure all your tracks are going into the master bus rather than direct to the audio device. Quick way to check that is to mute the master bus and verify that everything goes silent. Any tracks still heard are bypassing the master. This is assuming the master bus output is routed to the audio hardware, as it should be. Nothing else should be routed to hardware.
Then have a look at your export settings. Make sure the source is "Entire Mix", that all the options (e.g. track automation, track fx, etc.) are all enabled, and the format is Stereo.
There are other ways to mess up pan positions, e.g. setting the interleave to Mono or using a mono effect on the master bus. But those would also affect what you hear, not just the exported file.