Picking up stitches and knitting

I’m knitting a man’s sweater vest.
I have to pick up and knit stitches from the bottom right, up the right side, around the back of the neck and down the left side to the bottom left. Then, I have to knit a border/edging with bottonholes on one side.
I have ripped the border/edging out two times because - after binding off - the border/edging is “buckling,” for lack of a better word. It’s wavy and pulls the bottom left and bottom right upward…like the border/edging is too short. I hope I explained that well.
I don’t know what to do.
Please help!

If the border is coming out all right but the bind off is too tight, try this BO:

I have trouble with too tight bind-offs too. She demonstrates it with k2p2 ribbing, but it can be used with any configuration of stitches.

I’m not having a problem binding off. The problem is, I don’t know how many stitches to pick up and knit to make the border/edging lay flat. Mine keeps rippling.

Start again, but only pick up about 6-8" worth of sts. Then work the edging rows and bind off. See how that looks. The usual ratio is 3 sts for every 4 along the edges and 1 for 1 along the back of the neck. But your gauge may need 5 for every 7 or 2 for every 3.

It could be the spacing on the stitches. Maybe this will help.