Hii Chinnu!

There's no problem in pursuing BSc mathematics in another state. You can easily get admissions in Tamilnadu, given that you satisfy the eligibility criteria of the particular College you want to get into. If you specify the name of the College you are interested in, it would be helpful for us to specify its eligibility criteria. Some colleges provide merit based entrance and some provide admission after entrance exam. So, you need to study well in class 12th. Score good and then, apply for course in the College.

Hope this helps.

Good luck!