Hey,
If you are extremely good in maths, then you should pursue this field. It has ample of opportunities in various field of work. And yes, you can pursue BSc Maths after 12th. Some institutes insist on 12th with Science stream, but mostly they do take commerce students with Maths as one of the subjects in 12th. There would be some criteria of minimum percentage etc., and/or there might also be an entrance exam set by the college, so be prepared.
All the best.
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