You are right about taking it in the morning, your hormonal levels are highest then. If you had sex a week and a half ago I very much doubt that a test would show up positive, I think you are just going to have to wait it out because if you are pregnant , your just not pregnant enough for the test to show positive.. Do you kind of understand what I mean?
Also be careful girl if you dont want to get pregnant use some birth control. If your going to be sexually active at a young age you need to be responsible about it, having sex is a mature thing to do, you need to act like an adult if you are going to mess do it. Id say just be careful for the next few weeks, no smoking, no drinking, ect. When was your last period? And how far apart are your periods usually? I wouldnt really worry about being pregnant to much, just be careful until you know for sure and be careful next time you have sex.