Calcutta University don't offer UG courses at its own campuses. The UG course is provided by the affiliated institution of the university. Now depending on the course and the college, the marks requirement will matter as the admission to this colleges are on the basis of 12th marks. Now if you go for average colleges then you will get admission undoubtedly. For good colleges such as Asutosh College it can be tough.

To know about the colleges affiliated by CU visit the link below:

https://www.careers360.com/university/university-of-calcutta-kolkata/affiliated-colleges

I hope this answer helps. All the very best for your future endeavors!