Changes Haven't Saved when I Reopen Mp3 file

I keep running into this problem when saving a wav to an mp3. I work for an indie radio station that requires all the uploads to be at -0.1dB. I do this through applying a hard limiter on the wav file, then saving as an mp3. This works fine, but if I close the file out of audition then re-open it to check it, it's no longer limited to -0.1, it's hitting 0db and clipping. Sometimes the track length has changed too, usually by around 0.08s but I need it to be exact. I've also tried saving it as an mp3 first and then hard limiting it, but that makes no difference. Is there something in my settings I need to change? Is there an easier way to do what I'm doing than using the limiter? Thanks!