Science

The only way to crack maths is practice. You need to start practicing basics. Start from any good for CAT quantitative books like R S Aggrawal or Arun Sharma. If you find problems with these books difficult to solve than refer the maths books of 8th,9th, and 10th. In this way, you will be able to make your concepts clear. Quantitative part is as important as Verbal. Student good in quants will be able to tackle DI/LR easily.

Yes, final year students can also apply for civil service exams. But you have to remember that there are only 4 attempts in this exam. So better option would be to complete your B.Sc and then prepare for at least 1 year so that you can perform better in the exam. It is the toughest exam of India. So, you have to work hard to clear this exam.

Hi Sreeja,
The eligibility criteria for this courses are pretty simple. Please do visit the given link it has all the information regarding eligibility criteria.
http://www.sxccal.edu/admissions/SXCAdmission2017/UG2017/EligibilityCriteria.htm
One more thing to add is SXCKOL offers two courses in biology.
1. B.Sc in microbiology
2. Integrated M.Sc in biotechnology.
For the latter one, visit the post graduation part in the website.
You said you are from AP board, that's all right. Nothing to worry about. You have enough marks, you can make it to SXCKOL.
All the best.

60% is mandatory to get admission in any good college.

You need to score above 60% marks in order to get admission in a good college for B.Sc.