Congratulations on having watched Kokuhaku! I watched it two times already and wouldn't mind watching it for a third time.
The text is a disclaimer. It says: "This story is a fiction. Any phrases or actions shown should not be taken positively (literally) . Some merchandise, trademarks or characters may resemble stuff from real life, but are not used for commercial purposes or to damage reputation."
Also i hope you watched it with subs, not dubbing. Some lines are just so catchy. Like Yuko sensei's 「パチン、じゃなくてどっかーんて！」 and Watanabe-kun's「なーんてね」