Quote of a lazy and irresponsible man-
"The best way to escape from your problems is to put the blame on others"
Your friend have done the exactly the same thing. Mistakes are done by everyone. A man who haven't done any mistakes in his life is not fit for success.
Getting low marks in just one examination is not the end of you life. The more you do mistakes, the more you learn.
If you still have any problem with the teaching of your teacher you can straight away go to your teacher and report your problem. None of the teacher will scold or hurt you ask doubts.
So instead of blaming others for your mistake, rectify your mistake and give your best in next time.
Hope it helped you.