All Recently magazines are designed with a single wrap-around cover.
When selecting a photo for the cover, horizontal (landscape) photos will work best. You absolutely can use vertical (portrait) photos as well, just be sure to set the cropping.
To fine tune the cover cropping, tap on the cover photo on the last screen of the layout process. The cover photo will print exactly as you see it on the preview in the app (see below) when you tap Publish.