I am slowly working through the learning curve. I would like to make some corrections to the Google Earth file I made and saved. Can I edit this shoreline with the define map boundary button/pencil? I am noticing that when I regenerate the map, my shoreline is not wide enough to accommodate some of the sonar data.

You can drag individual points in the boundary around in the Define Map View (mouse mode select (arrow)), but other than that editing options are limited. Maybe better to do it in Google Earth for a bit more flexibility and reimport (delete the old boundary first).