Note: The gather used in this stitch pattern is a variation of the regular gather. It's best explained as working a central double decrease instead of knitting three together as the base of the gather. Naomi Parkhurst of Gannet Designs has a good tutorial that you can find here:
https://gannetdesigns.com/2018/01/22/gather-together-permutations-of-a-knitting-stitch/
Enjoy!
Shown with a cast-on count of 21 stitches.