Can you post a screen shot to make sure you aren't experiencing anything out of the ordinary?
In any landscape multi monitor solution there will be stretch (more commonly called 'Fish eye') on the outer monitors. There is little you can do about it if you stay in landscape mode. For one, you could lower the FOV but will eventually make make the game claustrophobic. The other is to push the monitors out flat but that is only to get it further out of your vision.. it's still there though. Basically in landscape mode you should only focus your vision on the middle monitor and use the outer as peripherial (not direct) vision.
If you have IPS panels you could turn them sideways and run in portrait mode. I believe that is the best solution for the Fish Eye effect.