If you want to go for a government University or college then go back to 11th and choose maths as an optional subject. Also if you are a CBSE/ICSE student you can opt your 6th subjec maths.
If that is nit the case work hard and secure admission in SRCC/ St Stephen’s which also have same value as bcom ( hons)
However if you have money then enroll in a private college/ University and you will be able to do hons without any problem.
But keep in mind you will have to work a bit harder for mathematics as you will have to start from ZERO in concepts like calculus which would otherwise have been studied by you in junior college years.