Did you forget to put it in the fridge? Did you use too much milk? No problem. If it’s too thin, just whisk it again and let it sit a little longer. If it’s lumpy (because you whisked like you were angry at it), just strain it through a sieve.
Pudding is forgiving. It won’t hold a grudge. You can even eat it warm if you’re impatient. Warm chocolate pudding is basically a legal form of child-like happiness, and nobody can tell me otherwise.