Short hair can sometimes make a round face appear rounder. It is possible to have short hair without adding volume to the face. A competent stylist will be able to find a style that suits your face's shape.
To avoid adding fullness to a round face, avoid a short style that has a lot of layers. Opt instead for a sleeker cut and keep the volume near the top of your head. Side-swept bangs can help to balance roundness. A smooth, chin-length bob without a lot of layers gives the impression that a round, full face is lengthened and thinned out.