CD 15, testing the last 3-4 days, still no +?

DH and I are TTC #1. According to this app, I'm ovulating today, but the OPKs all have been negative for like the last 4 days. Is it possible I ovulated sooner than that? It would have only been CD 10 or so.

Update: Got my positive opk this afternoon! But I have another question. I guess I wasn't wet enough last night when we BD'd, because DH had a little scratch on the side of his penis. Does that mean we can't try again tonight? It's like the perfect time, but I don't want to risk causing him any unnecessary pain.