Hello,
1/ Read this article – https://xstore.helpscoutdocs.com/article/89-product-images
It is recommended to use a graphics editor and prepare product images (make them the same size) before uploading images to your media gallery.
Also, it would be better to disable “Stretch product images option” option and re-upload images that are “too small” in large resolution.
2/ Screenshot from the demo – https://prnt.sc/hV3I-RZLrofq
Regards