how to show 3 columns ?

hi !

I have an issue. i’d like to display 3 columns on my homepage. the option to show 3 columns is activated. so i have the “left sidebar” option in the widgets section. so far everything’s fine.
but when i add widgets under the “left sidebar”, those widgets do not show on the homepage.
the homepage appears with the main column on the left, followed by a big vertical blank space (which should be the left sidebar i assume), followed by the right sidebar.
have you got any tips to share what could be missing ? even if it’s code

Thanks !