Gauge came out 10 rows to 3 inches, as desired, but 6 pattern repeats is 3 3/8 inches with green j hook.
Try with ergonomic L hook.

Started with chain 90 to make longer vest. 44 repeats.
Did increase rows on row 4, 8, 12, 16, & 20. Did first 14 pattern stitched with sc, 2 dcs, remainder with sc, dc.
Worked 31 rows in pattern before armhole shaping, not 30 as specified or armhole would be on the bottom.

Armhole shaping
Row 1: Do 12 (sc, 2dcs), then 20 (sc, dc) for a total of 32 pattern stitches leaving 17 unworked.
Row 2&3: 31. Row 4&5: 30. Row 6-9: 29
Total rows 40

Left back with same differences.

Front:
Completed row 8

Finally got back to this and finished it. I do still need to get more snaps as I can’t find the ones I bought.