I am not sure but I think it could be that unless the screen is wide enough tiddlywiki is responsive to screen size and defeats the changes you are trying to make.
Is it still a problem on a wide screen, and zoomed out?
The Stories plugin was packaged specifically for Stroll. It is not recommended for use in other contexts. In particular using it in any wiki with customized layout or CSS will require extensive CSS adaptation.
“The Stories plugin was packaged specifically for Stroll. It is not recommended for use in other contexts. In particular using it in any wiki with customized layout or CSS will require extensive CSS adaptation.”
You can remove the installed plugin again.
If it doesn’t help, you can disable your plugins one by one to see, if you get rid of it.
BTW: If you make changes, always backup your system before!
@JN33 you can use this button shared by @Brian_Radspinner to change the number of columns of tiddler contents (based on Shiraz)
Edit: I think I misread your comment. I thought it was for multicolumn layout of tiddler, while what you were asking was multicolumn layout of story river