You can certainly opt for commerce with Math because that will help you keep options like BCA open for you. While you say that you dont score well in math, try and find out what is the reason behind it. Is it just a plain mental block or it is the lack of practice.
Math is a subject that would need just practice and practice. So try doing that. You have understood what your problem is, so half the battle is won. And moreover math is a part of our daily like so if you are able to learn it by examples it will be easier for you to retain the formulas.
Hope this helps.