Hi Meghan, it actually looks like CD13 to me. The reason FF didnt give you the CH on CD13 is because on CD16, there was a bigger dip in your temp and it is taking that temp as the O day. I think on CD15, if there is no spike in temp, FF would give you your CH on CD13? Your CM shows fertile days from Cd10 to Cd15, so you probably O'd on CD13 but I'm just giving my amateur opinion.
But if you look at the larger picture of your graph, there is not much of a temp difference before O and after O isn't it? There was definitely something going on from cd11 to cd16 while your body was trying to O but I can't see the biphasic trend yet (?). Hopefully the next few days, your temp will get higher and stay there for 9 months.