Yes, you can, but from my experience I am telling you do B.Sc., science in standard 12th is quite difficult and you are almost going to revise these things in your under grad. you will have many opportunities, including the ones which B. Com students could do. You can make a career in medicine, technology, mathematics, statistics, there are so many un-ending possibilities in it. I have seen people leaving science after their 12th is just because its too much to handle in that time and all of a sudden the standard of study/education is raised from 10th to 11th, but trust me I moved to commerce after 12th science and when I saw the books of my under grad. friends (specially if you are from UP board, or ISC board, or CBSE board) I thought why did I leave!!!! , the things are almost same that were in 12th with a bit extra.
But…. if you really want to move into commerce and have a passion for accounting or economics or want to really make a future in it, go for it.
There are ample of opportunities you can do after that, like MBA, or CA, CS, but in this I would suggest do B. Com honors, rather than normal B. Com , because nobody takes it that seriously these days, there are so many other good under grad. programs like BBA, BBM etc….
I am sure you will figure out for yourself, what you want to do. Nothing is easy, if you have to make a career, you will have to work hard in both the streams…Just don’t be too hard on yourself… take it easy nobody knows it better than you what you really want.. But there are no short cuts for a prosperous future everyone has to work hard at the end..