That is because you are forcing the image to be centered vertically and horizontally when doing this:
Image {
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
source: "img/img3.png"
}
If you want your images to be centered horizontally but at the same time keep the layout in the column you should remove the anchors.verticalCenter
property from your Image
components