The ornamental design for a modular three piecel-shaped seating set, as shown and described.
FIG. 1 is a front perspective view of a modular 3 piece L-shaped seating set having a tall backrest configuration with cushions and accessories; and,
FIG. 2 is an exploded front perspective view of the set of FIG. 1 showing the three L-shaped pieces separated and one cushion separated for ease of illustration.