UI is too small and I have changed the UI scale in options.ini to 100

@carrallton  Try deleting the options.ini file entirely, letting the game generate a new one.  You'll need to reset your various options manually, but that's not too complicated.  Be sure to check the in-game resolution too—it should match your monitor's resolution or have the same aspect ratio.

If this doesn't help, you can make the UI bigger by changing its value to something lower than 100.  Try 75 and see how that looks.