Spray two half baking sheets and a quarter baking sheet with cooking spray. Set aside in the refrigerator.
For the strawberry layer: Combine the hot water, plain and strawberry gelatin. Once thoroughly combined, pour the strawberry layer into one of the half baking sheets in the refrigerator. After 15 minutes of cooling, add some strawberry slices, if desired. Allow the gelatin to cool until set, about 2 hours.
For the white layer: Combine the hot water, sweetened and unsweetened coconut milk, whole milk and plain gelatin. Once thoroughly combined, pour the white layer into the other half baking sheet in the refrigerator. Allow to cool until set, about 2 hours.
For the blue layer: Combine the hot water and the blue and plain gelatin. Once thoroughly combined, pour the blue layer into the quarter baking sheet in the refrigerator.
Once the layers are set, remove them from the refrigerator.
Turn the red layer out onto a parchment-lined platter or cutting board. Slice two-thirds of the white layer into strips and reserve the remaining third to punch out stars with a star-shaped cookie cutter. Top the red layer with the white stripes. With the widest side of the blue layer facing you, cut the layer in half from the top of the baking sheet to the bottom. Add one portion of the blue layer on top of the white stripes on the top left portion of the flag. Top the blue layer with the white stars. Using a piping bag fitted with a star tip, pipe out a whipped cream border and top with blueberries.
You can strain the gelatin if it doesn't dissolve after a couple of minutes of stirring.