Mix all ingredients for the Three-Berry filling and let stand for 1 hour.
To prepare shortcake:
Heat oven to 425 F. Mix baking mix, milk, sugar and margarine until soft dough forms. Gently smooth into ball on lightly floured surface. Knead 8 to 10 times. Roll dough 1/2-inch thick. Cut with 3-inch cutter.
Bake on ungreased cookie sheet 10 to 12 minutes or until golden brown. Split shortcakes; fill and top with filling. Top with sweetened whipped cream.