If your opk was negative yesterday, then I think you'll be fine. Of course it is possible that you miss it, but I think chances are good that you'll be okay. Don't forget that the egg lives for 12-24 hrs after it's released so even if you O as soon as tomorrow, you should be okay. You may not even O til Friday. Everyone's different. BD tomorrow night anyway for sure!! I read somewhere that when trying for a boy, some people don't BD til 12+ hrs after they O and abstain the days preceding O. Good luck!