I suppose it could be saturated, right at the edge of letting some remain undissolved, but hard to be sure. Do you have any potassium iodide left that you could add in small amounts till you get just a bit left over that won't dissolve?
Yes, add more. It's not too late. As far as dumping the previous 1/4" left over, that's probably a Trapper question, but offhand I don't think I would have dumped it. Just add more water and continue. It's probably preferable to start each batch fresh, but in an accident, I'd use the liquid I could and then add water and shake/stir till just a bit was left in the bottom of the container to indicate continued saturation.