I missed an AS level exam back in the day, I know the exact feeling. The college changed the format of the exam timetable, before they just put what time the exam started, on the new one they had what time it finished too. All I saw on my timetable was the finish time, thinking it was the start time. I got there just as the exam finished. I was pissed, i didn't even get a call.I got to do a retake in the summer, so it was all good in the end.