I got down to sewing and really took my time. Sewing together the fronts is MAGIC and I'm still smacking myself for missing that part.
Once I got both sides done with the first stitches at the edges of the zipper tape, I paused the sewing and undid the bind off on the collar. The zipper was definitely a bit too long and was causing the waviness. I knit a few more rows, bound off and then did the final sewing, carefully turning over the long bit at the top.
Not going to lie, that took a couple of tries to get right. No photos of the frustrating parts!
Then, I sewed an overcast stitch along the middle of the zipper tape to keep it neat and stable. I definitely peeked through the sewn up knit facings to make sure it was sitting right and that I didn't sew through the pink yarn I used to keep the cardigan closed.
Correction: after I sewed through the pink yarn that I used to keep the cardi closed, I started paying more attention to that detail...
Once the sewing was complete, I removed the pink yarn, tucked in the threads and admired my handiwork.
I'm so happy I took the time to fix this. Now this sweater is in high rotation in my wardrobe and I LOVE LOVE LOVE it.
No zipper showing: