My own design, pattern here.
Blocked size: 36” deep x 68” wide.

Shawl maximum size calculator here;

With your total number of rows you can then look at the pattern and see how many rows you need for the edge. Then you minus that from the total and you know you need to start your edging before you get that far.

How to work edge YO’s

Some people have asked about how to make sure the yarn overs on the right hand edge are the same as the ones on the left hand edge.
The issue is usually caused by forming a smaller yo when working p, yo, k than when working k, yo, p.

This is the method I use for the wrong side rows with the yarn overs are the beginning of the row (k, yo, p) and at the end of the row (p, yo, k).

See the bottom 6 photos for this project.
(please note in these photos were taken of a different swatch, only refer to the stitches on the needles, the existing rows of the swatch are in stocking stitch with no garter st edges)

When we do k, yo, p, as at the beginning of the wrong side row we tend to make the yo knitwise - as in we take the yarn under the needle to the front, over the top to the back and then because we are about to purl we bring it to the front again under the needle, then we purl.
(photo 5)
I think you have this bit just fine (as shown by the yarn overs on the left hand side of your photo).

When we do p, yo, k, as at the end of the wrong side row, a lot of knitters take the yarn from the front over the top to the back and then knit, this makes for a very short yarn over.
So instead after the last purl, take the yarn under the needle to the back,
(photo 6)
over the top of the needle to the front, then back under the needle to the back, ready to knit the next stitch.
(photo 7)
With the next stitch knitted our, p, yo, k, looks like this.
(photo 8)

When you turn around and knit the right side row, you will knit then do the first yo as normal, the next stitch you knit will be your yo from the wrong side row, you will notice it is mounted the wrong way.
(photo 9)
It’s really important to knit the leading leg (the one closest to right) which will be the back leg rather than the front leg. This is because of the direction we made that ‘p, yo, k’ yo on the wrong side row.
(photo 10)