Combine 3 Tablespoons sugar, margarine and crushed pretzels. Press into 9"x13" pan; bake at 350 degrees for 10 minutes. Set aside to cool. In a separate bowl, mix cream chess, 1 cup sugar and fold in the Cool Whip. Spread over cool crust. In another bowl, pour boiling water over Jello mix. Stir until fully dissolved. Add frozen raspberries. Pour Jello mixture over the Cool Whip mixture and spread to cover. Refrigerate overnight or at least 4 hours.