Hello Sarah
If you add an image to the block editor template using the "image only" block, there will be padding automatically added around the image, causing the image width to max out at 580px. If you instead add the image using the image manager in an HTML block, it will fill the entire width.
If you use an Image Only block, the image will always be centered in the block. If you use an HTML block, you can use the alignment tools in the block to reposition the image.