Hi I agree with Shan. You may have got a darker line had you tested again 4-6 hours later. OPK's can be a bit tricky for some of us to get a positive on. I would feel confident in saying that your surge was detected and usually you will ovulate within 12-48 hours after detecting it.
I say bd away for the next few days.
We will all be crossing our fingers for you!
Big Hugs,