Struggling to cohesively tie together the story at the 80% mark

Any advice for when all of your major scenes are written, but the story is not yet tied together because there's a handful of transitional scenes that need to be written to thread the story together? I feel like I'm ready for my official second draft... because a lot of major notes need to be taken care of (introducing characters earlier, changing world-building, foreshadowing events, developing characters more deeply, etc.) but I still have about 5 unwritten chapters. Every time I try to write them, they come out very unsure because they include the characters/worldbuilding/etc. that I know will be changed. So I'm hesitant of how to approach them.

How would you approach this? Write the first draft completely even though major edits will change what I'm writing? Or go back and flush out my major edits and see how that changes those final few chapters?