Based on the information it seems that you just stopped oral birth control pill and had sex after that, as well as you endometrium thickness is 11mm on ultrasound
, and wanting to know if you may be pregnant since you have not had full blow period and just spotting.
The answer to that question is sometimes it happens that spotting occurs to women coming off of birth control pill.
Here are two thing that can answer for sure wether you are pregnant or not for sure.
1) Wait for a week till you get a full blown period. It some times messes up the normal cycle.
2) If no bleeding, then take a over the counter urine pregnancy
test (where you have to pee on the stick to find out wether you are pregnant or not) do it after 15 days from now, if negative first time take same test after a week i.e 21 days from now and confirm it.
Hope it helps,