Thanks for the suggestion, Niek, but it's really ok if they do their map making in here if they want. That will stop a topic war between the two topics being constantly updated in the same forum, which would be very annoying.
Also, my math was incorrect and Xfixium is right about the proper scale dimensions. However, it won't make much of a difference and we're too far in to start over. The only easy thing I can do right now is to remember my mistake, and save xcf files next time.
By the way, an xcf file is GIMP specific and saves the file with all the layers separate, so you an return to working on the image without having to go through a lot of hooplah.