Try to crop your image to the same sizes ratio as the image container (square).
Here’s how: https://help.shopify.com/en/manual/shopify-admin/productivity-tools/image-editor#crop-an-image
If the image in media is too wide or too height and on site it will be square - the exceeding image will be cropped.
Also, if the image is with height or width smaller than the container, it will be blurred in the shop, because css will stretch the image, to cover gaps in the container.