Hi! When I ask Adobe Express for iPhone to generate an image, it generates something that look like an standing A4, with some white pillars at the sides. If I download or resizes the image, the white pilars are still there.
Could you let us know where you started the image generation process: from the "Home" page of the Express app, or inside the editor? It looks like it might have been the latter. In that case, you will want to choose a ratio that matches that of the page. It looks like the page is square (1:1) while you had picked (4:3).