Craig, not sure what the problem here is and your post is a bit odd. Using the latest (2.8.) version of Gimp, the 'Create a New Image' dialogue has the option to state your image size in width and length. You can select pixels, or inches, or whatever. You probably want to enter 7000 and 3778 and select pixels. I tested and there is no minimum size of 3, which in any case would not be an issue.