See the repetition is based on your choice and not necessarily your parents's choice. It is understandable that they might be in denial because you flunked class 11. But if you are not into humanities then you should not opt for the same. Try to make them understand that you want PCMB and you will work twice as hard for the same. They might give in to your heed.
Also in terms of opportunities both the fields are good and will require someone who works hard.

Best Of Luck!!!!!!!!