I like the way you form your reply by considering history of conversations

the only correct form is Я хочу сказать тебе, что or if you like to рассусоливать, then Я хочу сказать тебе то, что
That doesn't make much sense in English. "I wanna tell you that, that..."

We got "that" twice, that doesn't seem right.


Что? - То!
What? - That!

Not sure I get it -- if it ends with a question it's a что and otherwise it's то?