The twilight zone, right in my own house

Here's what I did:

Cast on, knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit knit cast off at underarm. Count.

What?

Count again, add on fingers, look carefully, count again.

There are two mistakes so far. Neither seems fatal, though neither can be explained by reason alone. Cue scary music.

Firstly, one of the columns of lace is two stitches closer to the edge than the other at the underarm, but not at the bottom. Did I really miss those final k2togs in the lace?

Hmm, it looks like I might have done that once.

The other problem is that I have 4 more stitches than I should have. Cue really scary music. Four stitches!? Four!!??

Lucky for me they are tiny and I can't see them looking obtrusive anywhere. I did all the proper cast-offs and decs at the underarm and don't want to go mucking about with that, because I have to set in the sleeves. I have to fiddle with the top of the back and shoulders anyway, because I added stitches to the width, so I will just have to fiddle a bit differently now.

Four stitches?? How did that happen?