You can opt for other subjects as electives, or if, you're interested, you can study with focus for a couple of months and you can cover enough ground to study UG level Chemistry or Physics.

Hii vidhi,
Your case is very common for commerce with maths student who want to pursue bsc hons mathematics.I know the procedure followed by Du , if you have taken an hons course then there will be a generic elective subject and that you can choose yourself such as history , eco etc.And in 3 rd yr there is no GE.
Hope it helps.
Best of luck.