Hi Akash,
                 Whatever you do, you have to atleast match the educational eligibility criteria whatever provided by the institution or entrance exam.

In such case, you booked seat but you get less marks in 12,you can't get admission in the college. Because in such case, if the college admit a student, the college will face problems further. You will not able to seat for the placement(if it will be professional degree) as well as to get the degree.

So, you booked seat but get less marks,  the booking fees will be refunded or not, it all depends on college policy, it varies. So, know about the all policy related that from the college.

Hope you get it & don't be negative. All will be good.
Best of luck for your future.