Once a scale is used an activity, you are unable to edit it. So, the "easy" way to fix it is to give any activities that use that scale a point type grade, and make the changes, and then change it back.
As an alternative, if you have access to the Moodle database, you can change spelling by editing the name field of the mdl_scale table.
While on the topic, make sure that your scale goes from low to high. For example, Not submitted,Submitted should be the order of the scale items to have grades work correctly.