What would you do if the surprise party was for you but you weren't suprised?

If the surprise party was for me, but i was not surprised,
I'm going to tell the truth that I'm not surprised in the surprise party that they made for me.
But!I would tell them that I really appreciated their efforts and hard works on how they prepare the party for me, and also, I would thank them.

And I know that what I did to them is wrong, and in return, I will treat them, so that their feelings would not be hurt.. And that's all :)