Hi @StaceMaples -- I apologize that getting your cover image the way you want has been frustrating. I think I have some information and tips that will help.
An image on the story cover (and other media panels in the story) has a focal point that allows you to adjust the position of the image within the frame. This eliminates the need to trim your image to an exact size. In fact, trying to use a specific image size (especially very thin images that are wide or tall) generally doesn't give readers a good experience. This is because your story needs to look good on a variety of devices with very different screen sizes and aspect ratios.
The recommended workflow for a cover image is to upload your original/large image, preferably one with a square or landscape aspect ratio like 1:1, 3:2, 4:3 or 16:9 (but it's not important that the image have exactly one of these ratios). Then click the gear and adjust the focal point to ensure the most important part of the image is always shown, regardless of the device size.
Hope this is helpful! Let us know if you have any additional questions about this.
Owen Evans
Lead Product Engineer | StoryMaps