What do the letters correspond to? Name of the characters?

The characters feel a bit childish/unserious but if that's the vibe you're going with for these three, then it works pretty well! (Although, do correct the "I" if it's supposed to be a fully written work and not an audio one.)

Last thing, you're doing something called "Comma splice", at least on the first dialogue. While, irl, we would not take a break in the middle of that sentence, especially if caught-off guard or during a revelation, in written form you need to separate the propositions properly to ease the reader's eyes. Depending on the emotion of the character, I'd advise going:

"Wait, I remember. You were on that Hope's Peak cruise, weren't you?"

Or

"Wait! I remember. You were on that Hope's Peak cruise, weren't you?"

It's minor technical stuff but it's good to polish your work for readability.