Appearance > Menus > Menu Item Settings > Submenu
The Submenu Column Alignment controls the alignment of the columns in the submenu (which is separate from the text alignment).
By default, the columns will align based on your language direction (for LTR languages, columns will align to the left edge of the submenu).
Note: this setting is only relevant for submenus where the content width is less than the submenu width. In general, that means full-width submenus where the columns in the submenu add up to less than 100%. If the submenu width and the total column widths are equal, all alignments will be visually the same. To change the alignment of the submenu, use the Submenu Position setting.
Do you want to create a centered content area with consistent margins regardless of the column widths? Use the Rows feature