That is a pretty good image from an old folder. You need to stop that down to get the edges sharper (if that is what you want). One side is worse than the other because when it unfolds, the lens and film are not parallel. You can try to fiddle with it, but there is no comparison with a Rolleiflex TLR, with its rigid box-like construction that keeps lens and film parallel. Even if you did get it aligned, the lens is still not very sharp at the edges. I'd just use it as it is and get a better camera if you want sharp corners.