Oh... Yes you can opt for science field in your 10+2 with PCB and Mathematics subjects as well and if you so like mathematics then yes there are students who do graduation in the field of mathematics after completing your 10+2 from science field. BSC Mathematics is a 3 year undergraduate program.

Refer to the site below to know more about the same..

https://university.careers360.com/colleges/list-of-bsc(hons)-in-mathematics-universities-in-india

This is a link to some of the finest universities which provide BSC HONS graduation degree in the field of Mathematics.

Best wishes. Thank you.