Preheat oven to 350 degreees. Spray 13x9 cake pan with nonstick spray. Mix cake mix, water, oil, and eggs on low speed for 30 seconds then medium speed for two minutes. Bake for 26-31 minutes. Remove cake from oven and using wooden spoon handle poke holes in cake spaced one inch apart over entire cake. Pour sweetened condensed milk over cake, spread into the holes and edges. Warm the caramel topping in microwave to soften for pouring. Pour entire jar over cake and spread into holes and edges. Place pan on cooling rack and allow to completely cool. Once cool, spread the whipped topping over cake and sprinkle the heath bits on top. Keep refrigerated.