Your individual appearance will determine if you have a small / flat bottom.
This feature may not possess the curves in this area of the body that others may do, with the derriere sitting more flush to the contours of the lower back and / or thighs.
Many people (especially women) prefer the appearance of pert buttocks these days, as it’s a common, desirable trend. It’s often felt that a fuller bottom is more aesthetically pleasing and clothes fit more suitably over buttocks that are more rounded and adequate in size.