This is caused by how the image was originally added to the template. If you added the image and changed the dimensions right away the image will appear to be missing one of the dimensions. Word reads this incorrectly and in turn stretches the image. You can tell your image might do this because it's missing part of the dimensions like the image below. Note, it shows the left as 100 but the right is blank.
Donate image showing missing dimensions

There is a method to solve this issue. We also have a video showing the process as well.
  1. Remove the image from the template
  2. Add the image back into the location you want to see it (You do not need to re-upload it to the editor, just select it from the editor again)
  3. When adding the image back in, do not change any of the dimensions
  4. Click Update
  5. Double click on the image
  6. Now, you can change the dimensions to your preference and both sides of the dimensions will populate automatically