You either had a surge the night before you tested or sometimes like me the morning test, a day before positive opks, gives a positive, keep testing. They say doing the test early morning gives false positives, best time is 2pm but I see you did 11am which should be ok. If your opk was negative next day you definitely had your surge. For some women it only lasts a few hours, others up to 2-3 days. xx