Slice about 1 cup of the strawberries. Halve the remaining 3 cups of strawberries and set aside.
In a large bowl, stir boiling water into dry Jell-O mix for at least 2 minutes, until completely dissolved.
To the 1 cup of cold water, add enough ice cubes to measure 2 cups. Stir cold water and ice into the Jell-O and stir until ice is melted. Refrigerate for about 5 minutes or until slightly thickened (consistency of unbeaten egg whites).
Meanwhile, cut the cake loaf into 10 equal slices and line the bottom of a 9x13 pan with the slices.
Add sliced strawberries and 1 cup of blueberries to the thickened Jell-O; stir gently. Spoon the Jell-O mixture over the cake slices, trying to distribute the mixture evenly. Refrigerate 4 hours, until firm.
Spread the whipped topping over the Jell-O cake. Arrange strawberry halves on top to make the stripes of the flag. Use the remaining 1/3 cup blueberries to the square of stars for the flag.