There are number of opportunities after Class 12 for maths student .
90% People will give you advice for doing Engineering but you have to learn one that whether you are capable of pursuing engineering or not . If you are dedicated to work hard then you should take 1 year drop and appear for JEE.
Leaving engineering, B.Arch is also a fancy course which is not much more popular like engineering but for sure you will enjoy pursuing it . You can apply for B.A, B.S.C, from maths field.
If you want be a programmer you can opt for BCA+MCA course.
You have so many 10+2 govt. jobs such as Army, Navy, Airforce. You can also apply for CPL programme also .
Goodluck I hope this helps you