I more or less get what direction that conversation between Jin-Ran and the senpai went but I'm still so confused. How did it jump around so much like that and still stay on the same few pages?
Because drunk, but also because, until the end, senpai was trying to avoid the topic of Jin-Ran liking her. It's a scary situation, as she explained.
Another factor was the server coming with their drinks—an easy excuse to change the topic to something less personal. 10/10 chapter here imo.
They both talk around how they just had an exchange of feelings, Jin-Ran happy to play along with her senpai. Eventually it's Gujou who can't handle the "storm," the unspoken tension, and drops the game mid-sentence to say just that. Jin-Ran, further showing how she's genuinely happy to be with Gujou, responds by pointing back to the art discussion in her response. Jin-Ran is also metaphorically going out to sea, she's only accepted it sooner than Gujou.
An important display of this is how she didn't immediately answer Gujou's question she stalled a little. I'm pretty sure they both knew why Gujou was asking the question, and both knew what Jin-Ran would answer, but there's still nervousness. For Gujou, she's worried about not knowing what to do even if "the piece is right in front of [her]." Meanwhile, Jin-Ran is worried about reciprocation as evidenced by what she says at the art museum "I hope that you'll come to think the same too." The final line of the chapter is also phrased as a question, "are you ready/do you want to go out?" not "we should go out" or "please go out with me."
It was a little hard to decipher at first, but their entire scene at the museum is about love. Gujou's crush on Ibuki and the growing relationship between her and Jin-Ran. Ultimately, I think Jin-Ran is very right. There is no right way to love or fall in love; if you enjoy being with someone, isn't that good?
Some people may not enjoy the very subtextual nature of this manga, but I'm here for it.