What OS are you using?
If you have a NVIDIA GPU, try using the control panel and change the resolution to 2560x1080. It should be similar if you have an AMD GPU (using their control panel)
You can also try editing the game files, not sure which one exactly but it should be possible.
I think the easiest thing for you ty try is using the command (in console ingame) - "mat_setvideomode 2560 1080 0"
If you still get the problem, try changing the launchoptions to:
Please reply if you're still getting problems