It's not the number of powers that makes him overpowered. It's how they work.
I just recently read this article on rational magic systems on Mythcreants which explains why your magic system needs rules and boundaries. For example, it explains that your magic needs boundaries so you can craft strong, believable conflicts in your story. It also means that your characters have to come up with smart ideas how to use magic to their advantage because it isn't just a deus ex machina solution to everything.
Another article on the same site gives great advice on how to limit any kind of magic or superpower, though not all of it is applicable to your world. Examples would be to restrict a power to only be usable during a specific time (say full moon) or with specific resources (there needs to be water nearby) or to give your power a negative drawback.
In your specific case, I'm thinking that it would be great fun if your characters first power was relatively "weak". This automatically makes him an underdog, which is a great trait for a hero. Then, also restrict his secret, second power so it is really powerful under certain circumstances but absolutely useless in any other situation.
Remember, that just having two powers instead of one gives him and advantage over other people, because they are always going to expect he only has one. As long as he shows his first, weak power, he can use the second one in secret all he wants because nobody is going to suspect anything. This is a really strong power in itself, so take advantage of that and in turn make sure that his second ability is as weak as you can get away with.
Sorry for bad english, I'm not a native speaker.