Since, at the very start, we learn about how his plan was to spend lunch that day confessing to another 14 girls. Then after she agrees to start dating as a trial, toward the end of the chapter he tells her straight to her face that
It seems to me like wanting to ask out others (even multiple at the same time) was always his intention. Don't get me wrong it makes sense for his character and his desire to write better novels, I just don't know what he was expecting to happen after saying that to someone who he started dating (even as a trial-run). Know what I mean?