So I'm writing a fanfic and I've written some pretty decent banter between friends during a school break ending with some slight trolling regarding homework. I'm really ptoud of it since it's like my best dialogue ever and I suck at dialogue, but now I need to fast forward to Ryu leaving the school alone and I have no idea how to start the scene (since I don't have the balls to rewrite the thing I already have done). Could I get sny ideas/recommendations/pointers of how to start the new scene?

Old scene ending for reference:

“Don’t worry, I’ll be free to play tomorrow and besides, even if you’ll lose, there’s always another Clash next week! Now let’s get going, the lunch break will be over soon. What’s the next class anyways?”

“Next is math,” Fumi smiled diabolically, “I hope you’ve done the proofs we’ve had due today…”

“Oh shit. Shit, shit, shit, shit, shiiiiit…” Ryu had to use all the strength he had to stop himself from jumping from the nearest window, “Heeeyyyyyy Fumiii…”

“Yeaaah?”

“Could you per chance mayhaps let me copy your proofs for math…?”

“I dunno,” Fumi asked innocently, “what’s in it for me if I do?”

“Literally anything, please, I beg of you Fumi, you’re like my only hope right now, I don’t wanna get kicked out of here like this…”

“I’m not really sure to be honest,” Fumi cut a little deeper knowing full well they didn’t have a single assignment due today, “you ok if I’ll just think about it for a few minutes or so?”

Does anyone else have the problem of not being able to write a story from start to finish. What I mean is I can’t start at the beginning because for me the story starts in the middle. So, I can start a story in the middle, because it comes up in my head. But if I try to start from the beginning I draw a blank, so I figured that I would just write until I have enough then put it in the right order later. It’s like a weird puzzle that starts in the middle and fans out. Does anyone else do this? And if so, has it ever worked out? And no I haven’t finished a story.

i wasnt sure what subreddit to do with this but i guess this is the one.

im aiming between 2700 to 3100 words and im currently in the 1200s. i have trouble whether or not my informational paragraphs on my character are too long or too short, and im not sure if im getting in the action way too quickly, or its just the short sentences i have within the sequence to attempt a intense atmosphere. ive read it over multiple times but i feel like peer input is what is needed the most.

i sit really uncomfortably with the fact that the conflict happens a half a page after the character focused page. when i read it aloud it sounds fine but i think about how others would read it. im a bit of a novice and ive been experimenting with pacing frequently, and i decided to apply my knowledge into this project.

summary: the pacing personally feels weird and i feel like im getting into the action packed stuff too fast.

this is how its going so far. (sorry for the grammar error lines, can't seem to get rid of them without changing the supposed lines.)

DISCLAIMER!! PLEASE READ!!
mentions of adolf hitler are commonly present in this story