Heat the oven to 350F. Cover a 9×13-inch pan with foil for easy cleaning, and spray it with cooking spray. Set it aside.
In a big bowl, put the cake mix, eggs, water, and oil. Use a handheld electric mixer on high speed for around 2 minutes. Pour the batter into the pan and bake the cake for around 23 to 25 minutes, or until a toothpick inserted in the middle comes out clean.
After removing the cake from the oven, use the round part of a wooden spoon to make around 75 holes evenly across the cake's surface, going almost to the bottom of the cake. Then, leave it aside.
In a medium bowl, mix the butterscotch topping and sweetened condensed milk. Pour the mixture evenly over the cake. Move a spatula back and forth on the cake's surface to help the mixture go down into the holes.
Cover the cake and put it in the refrigerator for at least 2 hours, or until it is cold. If you want to prepare in advance, you can store the cake in the refrigerator for a few days before eating it.
Before serving, spread the whipped topping evenly on the cake, sprinkle with toffee bits, and serve.