Are you tracking anything other than CM? I just temp so I am probably not the best person to answer this...but if you did O on the 8th and BDed on the 10th, well, it's possible.
Eggs live 24-36 hours (can't remember the exact number of hours...but think that's about right), and sperm can live anywhere up to 5 days depending on different things. Sorry, don't know the specifics.
And if you did O on the 11th, there may be a better chance as they always say to BD before I rather than after....but also keep in mind that every cycle even if you time everything right there's only a 25% that you will conceive.

and hope it all turns out for you.
(And please, if I am wrong on any of this, someone please correct me!)