Hey Niketan.

I suppose there should not be any problem because of the ATKT for you if you want to pursue 3 year law from the same university. If the university conducts an entrance exam, then you are only required to fulfill the eligibility criteria to appear for the exam. If not, then they must be taking admissions on the basis of your graduation percentage. Either way you don't have anything to worry. But make sure that whether they have specified anything regarding this in their brochure. You can visit the admission comptroller to make sure that they do not have any specifications regarding this.

Hope this helps. All the best.