Hrmm, um... does anyone know what DPI these are supposed to be in? For some reason, the .xcf is set at 72 DPI, which can't be right, because it's trying to print the overlay at roughly 9 inches wide. Setting it to 300 reduces the dimensions to something like 2.1 inches wide by .667 inches tall, which seems too small.
Anyone have insights here? This is the first time I'm using GIMP by the way (I downloaded it just to open this file), so maybe there's something I'm overlooking about the print resolution settings in that program?