Science

Yes dear, you are eligible. The minimum marks required is 50 % to qualify.

Refer to https://www.shiksha.com/courses-after-12th/science for more information.

20 days are enough for UET preparation, Just go through the UET syllabus and prepare accordingly. The previous year cutoff for desired courses is given below.
1. B.A (Hons.) Arts regular seat for general category:- Cut-off rank=1568 and Cut-off marks=205
2. B.A. (Hons.) Social Sciences regular seat for general category :- Cut-off rank=1629 and Cutoff marks=193

For forensic science, you need to have a Bachelors degree in Science or equivalent qualification. With BCA, it won't be possible to go for this course.

The correction cannot be made after the last date of registration process. Also, the admit card will be issued to only if you have filled application form correct as per the guidelines.

I hope this link will help you :
https://www.shiksha.com/science/colleges/m-sc-chemistry-colleges-india.

Basically, the entrance exam syllabus will include your B.Sc. (Bachelor of Science) course material. Here is the link you can go through- https://www.shiksha.com/science/articles/how-to-prepare-for-top-msc-entrance-exams-blogId-13489.