To confirm O, you need a thermal shift and a cervical fluid dry up per TCOYF rules. It looks like you had a slow rise too, which can take an extra day to confirm O. Watery CM is more fertile then creamy CM, but I don't think it is as fertile as EWCM... I recommend getting the book. It does a better job at explain then I am. FF doesn't really do well with slow rise thermal shifts. I often have slow rise shifts and it always gets my O day wrong.

For me, FF said I oed on CD 16 last cycle and nothing I could do could get it to change it's mind. I actually probably Oed on CD 18 because of the spotting I had that day. (I had to stop checking CM internally due to a procedure I had on CD 17, but the spotting indicated a peak/high fertility day and 12 days later AF showed up right on time. I would have been 2 days late if I went with FF)
Oh, as far as opks. I see lots of women have trouble interpreting them, so I personally wont use them anymore. But that's just me.