Go to the menu where the menu item needs to be widened

Select the parent menu item of the drop down that needs to be widened. Then select the Fusion Menu Options link
Enter the width you would like to have the drop down
Save and close
Go to the menu where the menu item needs to be widened

Select the parent menu item of the drop down that needs to be widened. Then select the Fusion Menu Options link
Enter the width you would like to have the drop down
Save and close