So, here is how it all works for most girls timing wise. The first day of your period is cycle day 1. You begin counting from there. You get pregnant at any time during your cycle but the 'fertile window' usually starts around day 10 and lasts about a week. So, day 11 of your cycle was in the fertile time frame. Sperm can live for up to a week inside of you is why the window is so large. However, you used a condom!! That's great and keep doing that. Unless there is a condom failure, it should protect you against pregnancy and std's. Remember, when you are young, it is very common to be irregular! AND, stress can also impact things. If you feel you are too young or this is to nervous making for you, hold off on continuing to have sex. Don't get pressured into it. Also, just for information purposes, symptoms of pregnancy do not start immediately. It takes a while to have enough hormones in the system to cause the symptoms.
I personally would be shocked if you were pregnant so would not worry. good luck