Resizing columns
The maximum size of a row is 12. Suppose you have two equally sized columns with the total size of 12, and you add an extra column, then the maximum size has been exceeded. What happens is that the extra column is moved to the next row and, by default, assigned the value 12. This is illustrated in the picture below.
If you want all three columns to appear within the same row with the same size, you must manually adjust the size of each column and give them the value 4.
To resize a column, select the column you want to resize. On the right-hand side, expand Layout and select a size.
The unit of measure used for the size of columns is relative, where one unit is one twelfth of the total size. Because the total size is 100 %, then one size unit is 100/12 = 8.333 %.