So of course it's the morning of the big party, I woke up early made the cool whip frosting and even made my cake last night to save time. The cool whip frosting is ridiculously thin! How can I thicken it???
this is the recipie I followed....
1 cup milk (cold)
3 ozs pudding (flavor instant, mix)
1/4 cup powdered sugar (optional)
8 ozs cool whip (thawed)
1Pour milk into bowl and add pudding and sugar.
2 Beat with wire whisk 2 minutes.
3 Gently stir in Cool Whip.
I use a similar recipe that has cream cheese in it...
If you have that, add half a bar to start.
If not...maybe extra pudding mix?
Also...next time make your frosting at least a day ahead of time to allow it time to sit in the fridge and thicken naturally.
Not familiar with that recipe, but here is a Cool Whip filling/frosting recipe that can be a "back-up plan" . 
Using the wire wisk attachment, blend together:
8oz cream cheese
1/3 cup granulated sugar
2 Tablespoons powdered sugar
Scrape down bowl, then add:
1 large tub (16oz?) thawed Cool Whip
1 teaspoon Creme Bouquet or Vanilla
Whip on Med High for a minute, scrape bowl, then continue to whip on High for another minute or two. Don't overwhip!
Good Luck!
This is the recipe I use.
1 cup heavy whipping cream
1 (3.5 ounce) package instant vanilla pudding mix
1/4 cup milk
1 teaspoon vanilla extract
3 cups frozen whipped topping (such as Cool Whip®), thawed
Directions
Beat the whipping cream, instant pudding mix, milk, and vanilla extract together with an electric hand mixer in a large bowl until soft peaks start to form. Lift your beater or whisk straight up: the mixture will form soft mounds rather than a sharp peak.
Fold the whipped topping into the whipping cream mixture to evenly mix. Refrigerate until ready to use.
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