I noticed when I add a parallax effect to an image, the image gets very big and some of it gets hidden, what am I doing wrong?

After testing a little, basically i need to create a dark boarder around the part of my image i will lose so i can preserve the main part of my image.
I find this rather wrong, wix should of stretched out my photo not cut it from the bottom, something is off, i feel it could of been handled better.