Dear Student,
I want to tell you one thing, if you take a wrong decision in your life you have pay for it for your entire life.
Now coming to your question,
You are in a  very critical situation, that's why you have asked this kind of question, I can understand.
You are telling that you haven't studied anything in PCBM in your class 11 then how did you pass your class 11 final exam?
Okay keep that question aside.
See I'm going to tell you the basic things.
You can't change your subjects because class 11 and class 12 have same subjects for a stream like science or commerce.
You don't have any other choice you have to continue with your subjects which you have chosen in class 11.
Nothing has been gone to wrose. You can still fix this by your own.
You can start preparing for your class 12 in the summer vacation. Class 12 subject contents are relatively easier than the contents in class 11.
I know there are some topics which are important to learn in class 11 for getting the basic concepts clear for class 12.
Class 11 and class 12 are linked.
But there are some chapters and topics which have no relation with class 11.
And if you face any trouble in understanding any topic or subjects you can consult with your school teachers or take a private tuition.
But if you want to preform well in entrance exams then you have to take a year gap. As you are not clear with your basic of class 11.

At last I want to say work hard.
Hardwork beats intelligence.



ALL THE BEST !!!!!!





Thank you