I struggled for easiest program in xam.But was perfectly prepard.Did silly mistak.im very disturbd.pls help!:(?

I am an engg student(comuter science).I had graphics lab this year and I was enthusiatic & confident right frm the beginning since we had to do an individual project.Mine was infact the best one and my graphics project was the most efficient and up to the mark.Did everything on my own,helped all my frnds to do their projects too.Lecturers were also very happy and impressed.i was very confident on th day of xam.I had to show a demo of my proj and also do a lab prog.I got the easiest program of the lot.A dead easy program. But I couldnt do it for some reason!.I probably did a silly mistake in the program and struggled to get the output. All the others had left the lab but I wasnt getting even a single line on the display.I was getting a blank display. I started crying there itself.Even examiners couldnt figure out wat the mistake was!!. Finally the lab istant helped me by cross checking in the text book secretly and I could show my output to examiners after 1 hour. Now I am feeling very bad. Dont know why such a thing happened. teachers are very angry at me. I feel I ve suddenly lost my confidence. I feel very unlucky now.Why did such a thing happen inspite of me trying my best, knowing all the required things, getting easiest question in the exam and being capable too.now I dont have mood to study for remaining exams. What to do?..Am I very unlucky or overconfident or is it simply because I didnt concentrate at tht moment.Please help me.