If you were knitting in the round (it sounds like it as you knitted every row/rnd) and switched to dpn to continue in the round, you might have accidentally started going the other way. I think you should be able to see a hole or something where you switched directions if this is the case. If you have garter stitch and were knitting flat then you knitted every row; if you were in the round, then you had to alternate knit and purl rounds. If you really have stockinette on the inside then you have reverse stockinette on the outside. Confusing maybe but the distinctions matter.
Happiness is catching that dropped stitch while it's still fixable..