Preview image cut short

Hi guys, I hope you have a wonderful day

I have two problems, first is my preview imange got cut short even though it is 1600x800 which is exactly like the guide instructs. Second, my screenshots in a zip file just wouldn't show on my page store tho I had tried re-upload again and again. Can you please help me with this.

What is the format of the screenshots in de zip file?
Are all image files located in the root directory of the zip file and not in a sub-directory?

Could you try uploading 800x400 instead for the preview image? What is the file type?

1. The format in the zip file is all png
2. Yes, all images located in the root directory
3. I've uploaded a 800x400 but the preview image is still cut short, the file is PNG

Thank you for the respond!

Update: My screenshots have shown in the page, but the preview image is still cut short despite I have uploaded a 800x400 version. Please let me know how to fix it.