Fun fact: this is a known, universal effect of the way camera projections are simulated in 3D games.
It's aggravated, however, by higher-than-normal FOV and very wide aspect ratios. Though we provide the option for wider-than-normal FOV in the Options menu, I really don't recommend messing with it unless you're one of those people who gets motion-sick at certain FOV values.
If you're on a 16:9 monitor, you're just stuck with a certain amount of this.