What you describe would only happen if you upload an image that is not pre-sized to fit entirely within the maximum dimensions allowed, which would be up to 700px wide and 525px tall. I am thinking you may have uploaded an image sized to fit within 700px tall and 525px wide (swapping the dimensional limits). Since your product image is in portrait orientation (taller than wide), we would recommend making a copy of your original image resized to 525px tall (width proportionate) and upload that in place of the currently uploaded image.
