It's been awhile since I've played Skyrim but there should be a 21:9 fix at Nexusmods. The fix could be adjusting the ini files or a mod via the mod manager. I'm not on my home system so I can't check but look at that site and see if there is a fix.
Edit, found this.
It's been a couple of years since I last played Skyrim but that one doesn't look like the one I used. Did you follow the directions exactly?I tried that mod and it didn't work, but it could be I did something wrong. Was this what you used?
Yea Bethesda isn't really into 21:9 gaming apparently as I've had to make changes to there other games as well.I just received a new monitor and PC last week, so mod conflicts aren't the problem. I guess I'll just have to play around with it some more. I'm surprised Bethesda hasn't resolved this issue. It wouldn't require a major update.