Chosen Solution

While not a major issue, the neckline on my cotton Patagonia sweater is looking scruffy as the elastic has stretched and warped. It now looks all wavy as seen in the picture attached. Is there a way to make it look tidier?

I am surmising you don’t sew. I would take it to a dry cleaners and/or repair shop, where a new neckline can easily be put on. Unless you have a local handy sewer nearby. Look at want ads etc in the local paper etc. Good luck.