Hello,

Choosing a particular stream in class 11th is the toughest decision for a student because it makes the further path you have to follow. But sometimes students end up making a wrong decision.
As you have opted for PCMB you have both the options in your hand. But changing stream is a difficult task because every school does not provide the option of switching your stream. There are few schools that provide you an opportunity to change your stream within 1-3 months but you can not change it after your first exams.

But there are some schools that do not provide this option. As you have PCMB and not interested in medical, you may focus more on maths and built career in it. But you cannot leave biology if it is not your optional.
Hope it helps.

Good Luck!