Cut off both ends of the watermelon, leaving a large middle section to form the cake. Remove the remaining rind, pat dry and place your cake-shaped watermelon on a cake stand. Frost using the Cool Whip, then on the sides press the shredded coconut into the whipped topping. Core and slice six large strawberries in half and place around the edge of the top of the cake, add another strawberry to the center and add blueberries in between the strawberries. Chill until ready to serve.