There are many options you can opt after completing B.Sc Mathematics. You can go for M.Sc as the subjects that you have studied are popular ones, If you wish to enter engineering, the option is to do an M.Tech. However for M.Tech you will require M.Sc in Maths or Computers or Electronics.
If you are interested in teaching profession only then after M.Sc you can go for NET, P.hd.
If you are interested in the corporate world then you can go for MBA in desired specialization.
You can choose any of the option as per your interest.