<human>: Can you give me the gist of the text in a nutshell?

So currently I'm retaking science in year 11 because I'm dumb and didn't revise for science during the first exam during year 10, this caused me to get D grades.  
This year I have been revising a lot for this exam and I was fairly confident that I was going to walk out with C grades for all 3 science exams; however this morning I woke up to my parents shouting at me telling me I've failed my chemistry exam and at first I was really confused, I thought that there might've been some kind of mix up. The first thing I did when getting out of bed was check my timetable and I was sure as hell that my exam was at 1:30pm like the rest of my science exams but it turns out when looking at my timetable that my exam started at 9am.  
So now I'm really angry with myself, now that I've screwed myself over and I'll probably need to retake my GCSE exams because I've made a stupid mistake by reading the timetable wrong and not double checking. I'm also failing most of my other exams, so I'm approximately 80% sure that I'm not passing 5 other exams to get into a decent college for the course I've wanted to do.
<bot>: I missed my chemistry exam because I read the timetable wrong and I'm now probably going to be a failure as I'm not clever in many other subjects.