Ripped out entirely and restarted to be larger, casting on 74 st, which works out to +18 st (+6 on the front & back, +3 on each armhole). Knit to about 8” below arm opening and tried on - it was a bit too generous and I was running out of yarn, so ripped back to ~2” below arm opening and started decreasing 2 st on each side every 5 rows.