if you don't want the watermarks, why don't you just turn them off?
You have extra space allocated on X axis. To remove, move your mouse over the X axis, right side. MT should highlight the X axis. When it does, click and drag to the left. That should remove the extra space.
the dropdown list for chart templates just shows you the history of the last ones used. If you have duplicate names for the templates in the list, then you must have templates with the same name but stored in different locations. There is no way to directly modify the list (can't change history, right? ). However, if the underlying file is no longer there and you select the entry, MT will prompt you and will remove the entry from the list. Other than that, you can change the chart to the 10 templates you wish to use, Those will get added to the list, pushing the others off.