Each wiki's main page, unlike other pages, does not contain additional blocks on the right side (recent wiki activity, latest photos etc.). So the main page becomes too wide. However, you may want to add your own right sidebar. Here is instruction of how to make a two column text on your wiki page.
Simply insert the following tag at the beginning of the left column
And the left column content afterwards. At the end of the column add
Right after that the right column starts with
Similarly, it is ended with
Note: These tags can be applied to any page on your wiki, not only the main.