If you are highly interested to pursue B. Tech in Vellore Institute of Technology , then you need to leave your B.Sc (Mathematics ) and start from the first year in VIT since it doesn't not offer any lateral entry.

But if you don't want to waste your one year , then you should check out for colleges which offers lateral entry in B.Tech . As far as I remember Indraprastha University in Delhi offers B . Tech lateral entry . And you can search for more colleges.