Yesterday, you and a friend were talking about a TV singing competition you both like. Your friend predicted which contestant would win. She was right. So today, you tell her this.

You totally called it! 真（完全）让你给说中了！

One of the meanings of “calling” something is to make a correct guess or prediction. When someone correctly guesses a future event, you say “You called it!”
你说中了，你猜对了，你预测对了。

In the example above, the speaker’s friend correctly guessed who the winner of the singing competition would be. So she “called” it. This is an expression that’s used in casual English.