Preheat the oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.
In a large mixing bowl, combine the cake mix, water, vegetable oil, and eggs. Beat on medium speed for 2 minutes until well blended.
Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then remove it from the pan and let it cool completely on a wire rack.
Once the cake is cool, use the handle of a wooden spoon to poke holes all over the top of the cake.
In a medium bowl, dissolve the strawberry gelatin in 1 cup of boiling water, then stir in 1 cup of cold water. Pour the strawberry gelatin mixture evenly over the cake, making sure it seeps into the holes.
Repeat the process with the blue raspberry gelatin, using a separate bowl.
Allow the cake to chill in the refrigerator for at least 2 hours or until the gelatin is set.
After the gelatin has set, spread the whipped topping evenly over the cake.
Decorate the top with sliced strawberries and blueberries to create a patriotic design.
Slice and serve chilled.