If I were less lazy, I would go straight to Option A: Change the plying head and drive band back to the normal ones, spin approximately half the remaining singles onto another bobbin, then going back to the plying head and drive band and spin more 2-ply yarn.
But I am so, so lazy.
Option B, for the truly lazy, is to use the remaining singles as weft yarn. I actually have a warp on the loom right now that would work with this yarn. Option C, for those who enjoy creating small Granny balls of yarn for display, is to chain-ply the remaining singles and finish with roughly enough 3-ply yarn to make a little hat.
What would you do?
Practical Margy is leaning toward Option A, just because it would be so nice to have enough two-ply to knit a lacy shawl. But Lazy Margy has been trying to be more authentic, lately, so I'm veering toward a nice ball of 3-ply. (Could I really be more lazy? Probably.)
Meanwhile, for your consideration, about 400 yards of 2-ply BFL/silk.