My problem is that I am trying to upload my images with the same size as the one that comes in the demo images, but these look different when I upload them (I left a sample image there).

cushion cover is my 740 x 1000px image (which is the same size as the demo image) and Decoration wooden present is the demo image (this image looks good), I say this because of the difference in size and quality that the images are seen; I am also exporting to the same format which is JPEG