You can adjust the width of both the static columns shown in the left part of the matrix and the width of the dynamically created columns in the right part of the matrix.
In Matrix Properties, select the Grouping page.
Select the appropriate row group, and click
In Group Properties, select the Format page.
Enter a suitable number of characters for the column width.
Save your settings.
In the Matrix Properties, select the Data page.
Select the appropriate column, and click Column Properties.
In Column Properties, select the Format page.
Under Column Width, enter a suitable number (in points) for the column width.