Okay, in Mendix Studio Pro,
1. you firstly make the home page, and add from add widgets layout grid.
2. you choose the layout 3-3-3-3
3. You see now four columns with auto-fill in the topbar
4. Double click the on the autofill topbar
5. a pop-up screen will open with the following:
Choose manually, and adjust the columns, If i am right it should be filled like this, but you can always test for yourself, if you want to have the whole wire frame add action cards from the add building blocks to the columns