I am glad you figured it out. I had already prepared a reply, so I will post it for others...
Once you selected the one wide column, all the elements or “gadgets” that were in the other columns were forced into just one column. Now when you edit the layout and choose more than one column, your gadget boxes are still in the left column which has gotten skinner to make room for the other columns. You can’t see the other columns because they do not yet have anything in them.
To move the gadget boxes from your left column to the other columns in the new layout, just click the title bar of the box and drag.
Hint: When moving a gadget from lower in the stack to a new column, drag it first to the top of the row and then over. When the shaded rectangular area appears behind it, it is ready to drop in the indicated location.