Great interpretation indeed. The words rhyme. I'm touched.
I have little confidence, though,
1. "Acchi-!!" or "Acchicchi-!!" usually used when touching hot stuff (like ouch or oops). And Mami also moves her finger down (to take the temperature) and up (Acchi-!) in the movie. But I don't know why the soda is hot (I wonder it's kind of common happenings on school festival or just Mami's trick).
2. After some accident happened (Acchi-!) the girl seems coming closer to the guy (Mami acts as...meta-perspective. refer to DLC) suddenly (or he moved closer to her, according to hypothesis 1.). He decided to tell her at once.