Hello,
Hope you are having a nice day. Here is limit – 6 columns for mega menu http://prntscr.com/hb52u2, but if you need 8 columns, you may create static block using VC, for example, http://prntscr.com/hb54l3 > create custom widget area and add the static block – http://prntscr.com/hb5580 > select the widget for the menu item http://prntscr.com/hb57w0 > http://prntscr.com/hb5842
Regards
