Preheat oven to 350 degrees F. Grease a 9×13-inch pan. Bake cake according to package directions. Cool cake for 5 minutes.
Dissolve the gelatin in the boiling water. Poke holes all over the top of the cake with the end of a wooden spoon. Slowly pour the gelatin over the cake so that it seeps down into the holes.
Cover and cool in the refrigerator for 30 minutes.
In a large bowl, beat cream cheese until fluffy. Beat in sugar. Fold in whipped topping. Spread over the top of the cake.
Top with blueberries and strawberries to form American flag.