Bunny Girl Senpai movie thoughts

So first "bomb" is the reveal why Sakuta (MC) has the scars on his chest - it's cause he donated his heart to Shoko (girl he first fell in love with)

then, Shoko reveals that she gets his heart cause Sakuta died in a car accident while otw to meet Mai
stuff happens, Sakuta is about to get run over, Mai appears from nowhere and saves him and she dies instead
10 min ish of grieving, then Sakuta gets a chance to go back to the day before he dies to save Mai by the power of Shoko's time traveling(?!?)
more stuff happens, Future Sakuta convinces Mai to trust him and not save him from the car accident, Future Sakuta then saves himself as his past self was about to be run over. Future Sakuta dies, but past, now current, Sakuta lives
all is rosy, but now Shoko is going to die cause she needs a heart transplant to live.
BUT this is the part i don't get. The middle school Shoko (the one you see throughout the anime) is still considered the "future" Shoko, so you need to go back to the past and "save" her . . . somehow.
Not much is explained about how past Shoko is saved, but because she's saved, Sakuta's whole anime journey is undone (cause it all started when he first met Shoko in the 1st ep)
but ofc, Sakuta still befriends everyone and Mai is still his gf somehow, and movie ends with him meeting Shoko at the beach (where he first met her in the beginning of ep1 anime)
lots of emotional scenes, but no time to digest it and the reason why/ how he saved past Shoko, makes the movie less enjoyable for me . . .

All these events happened over 2 light novels. I think they should've adapted this into several eps. Cause this was all over in 1hr 30min