you're imagining it.
taking a single mono track and panning it in the middle....makes the volume equal in both speakers. Which in turn makes it sound like it's coming from the middle.
Taking that same mono track, duplicating it and panning both tracks hard L/R...makes the signal play out both speakers evenly. Except now, because of Pan Laws (look that up, btw), it sounds louder. About +3dB louder. But it still is coming out both speakers evenly, and from what we deduced above...if the sound comes out of both speakers evenly, it sounds like it's coming from the middle.
So in other words, all you've accomplished is making the sound louder. And wasted hard drive space
If you want to work on doubling, you'll just need to record it again...or play with phasing tricks (ie. chorus, or nudging one of the tracks slightly).
If you want to make it sound wider, you'll have to work on the mix some more. A combination of delays, reverb, stereo wideners, etc. can help with this.