"No! No, you haven't upset me at all!"

That might not be the most convincing statement ever, considering Inigo's face is still very red.. But he just can't even bear the slightest thought of Taiki assuming he must have upset Inigo. There's nothing to do other than to deny that as quickly as possible and try to make sure Taiki doesn't believe that.

So he quickly rambles on, as if saying more will do more to convince Taiki. "It's fine! I--I'm fine! It's just.. me and my dumb big mouth!"