In a large bowl, toss the strawberries, sugar, and Sweet’N Low. Cover. Refrigerate until ready to serve. Preheat oven to 450 F. In a large bowl, combine the first 5 ingredients. With a pastry blender or 2 knives used in scissor fashion, cut in the margarine until the mixture resembles coarse crumbs. Stir in the milk and sour cream to make a soft dough. On a lightly floured surface, knead the dough 2 minutes. Press to a 3/4-inch thickness. With a 2-1/2-inch round cookie cutter, cut into 12 biscuits. Spray a cookie sheet with nonstick cooking spray. Place the biscuits on the cookie sheet 1 inch apart. Bake 10 to 12 minutes, or until the tops are golden brown. Cool on a wire rack. To serve: Split the shortcakes in half. Spoon 1 tablespoon whipped topping onto the bottom half of each shortcake. Top with approximately 2 tablespoons sliced berries. Replace the tops. Arrange the remaining berries on top of each shortcake.