If you are wiling to go for the BSc Economics course in Kolkata, then most of the colleges in Kolkata requires Mathematics as one of the subject in 10+2. If you don't have Mathematics then I would suggest you to go for the course of BA in Economics course because in this case, there are not much of restrictions regarding the Mathematics in 10+2.

Although this course of BA Economics isn't offered by most of the institute in Kolkata. There are only two institutes in West Bengal which offers the course of BA in Economics and the name of this colleges are-

Guskara Mahavidyalaya, Burdwan

Chandidas Mahavidyalaya, Birbhum

For more information regarding BA Economics consider the link below:

https://www.careers360.com/courses/ba-in-economics

For more information regarding BA Economics colleges in India consider the link provided below:

https://university.careers360.com/colleges/list-of-ba-in-economics-degree-colleges-in-india

I hope this helps. Wish you a great eve!