So like, I played it through once and found these. I'll play the other paths when I have the time. I skipped mentioning the ones Reikun already found. Sorry this is kinda long, but I hope it helps!
Oh, and sorry if it sounds nitpicky at times. You are a really a wonderful writer
I told her her town was a butterfly, waiting for Summer to flutter her glittery wings. (Near beginning)
While grammatically correct, writing one "her" after another made me confused the first time I read it, haha. Maybe add "that" after the first her?
EDIT: Waaaay at the end of this post, I wrote that you do not need to capitalize the names of seasons. I did not mention that in this line because in the song's lyrics, it sounds like Summer is a personification of the season summer, so you can chose whether to keep it capitalized or not in this line.
He doesn't even look over his shoulder, he just storms off. (Bumping into ex-band member)
Insert an "and" after the comma to fix this run-on sentence.
She huffs and I seem to have lost any attraction I have for her. (meeting Nancy)
Change to "to" because "for" implies that Rhyme feels attraction towards Nancy rather than the other way around.
But I'll be here just for one week. (A choice in first convo with Nancy)
Would sounds better if you switched those two words.
I...Don't know. I don't know if she'd like them. (Talking with Karen in her room)
Shouldn't be capitalized because it's not the start of a new sentence
But what did you think about it? (Karen and Nancy talking in the cafe)
Should be "them" because they are talking about multiple songs
A moment when I'm either going to try too hard or give up, no middle ground. (At music store)
You don't really need the comma and the comma makes it a run-on, so maybe replace the comma with "with."
I know it, I know it. I've been here before. (right after previous line)
People usually just say "I know," so getting rid of it would make it sound less weird.
It's not the weight I'm used to, and it won't sound the same, but, how different can it be? (same scene as last two)
The last comma isn't needed.
Karate Kid plays guitar and has to battle it out with the devil with the power of rock? (the audition)
Add "The movie where" at the beginning of the sentence and change the question mark to a period.
Can you remember it? (right after previous line)
Grammatically correct but another sentence could fit better here. Maybe replace with "Don't remember it?" or something
...(his name turns out to be Brian) (soon after previous line)
Reword. My suggestion is "whose name is apparently Brian" but you can roll with whatever you like
Peter has physical therapy today, otherwise he would have received it himself. (returning the guitar)
It's a run-on. I think I'd be best if you changed the comma to a period to make this two sentences instead of one.
Could you tell me how to get there, anyway, please? (getting directions to the hospital)
You don't need the comma before "anyway."
Being a very indignified dancer of the same myself, and knowing it sucks to have witnesses I do the only thing I can. (putting up posters with Nancy)
You need a comma after "witnesses."
Depeche Mode's Enjoy the Silence (back at the cafe)
Put double quotations around song titles. I think she mentioned the song's title when singing earlier too, so you'll need to double quote the title there also.
It's a rather tiring job, as not only you have to carry the crates inside... (after previous scene)
The bolded part sounds oddly worded. I suggest "because not only do you have to"
Was she...has she...did she say anything to you these days? (talking with Candace)
I would change it to "recently"
Then, it's like a storm breaks out (during the concert)
I think "Then, it's like a storm is let loose" sounds stronger, but breaks out works too. You need a comma after "then" though.
Today is my last day on Silver Shore (after the concert)
Change "on" to "in"
You can come back on summer (talking with Karen)
"On" to "in the"
I'll, I'll come back in Summer ("Paralell" Universe ending) <---"parallel" is spelled like this btw
There should be a "the" in front of summer, and seasons do not need to be capitalized
Silver Shore is beautiful in Summer. And in Winter. And in Spring.
same as above
I...Can't stay
This is technically one sentence, so "can't" does not need to be capitalized.
✧ 
✧ 
