CBSE 12th

Can you mention your stream and interests? Ideally, you should follow your interest and future plans. You must enjoy, what you study to be successful in your academics and career.

You can go for B.Tech and if you interest in a particular field, then B.Sc is also a good option. B.Tech from a good engineering college will be a better option, as you will have option to go for higher studies in M.Tech/ MBA or you can also fight for IAS/IES. You can grab a good job offer, as many colleges provide a good placement to students.

Which branch would you like to join?

Hello Ipsita,
You can request the principal along with your guardian. If the reasons are genuine, they should allow you to appear for the examination.
Alternatively, you can drop an email to the board authority, who will be conducting the class 12th board examinations. In last, you can seek help from the education minister of your stake, if you're capable to raise the issue up to his level.

If you are able to choose a particular field, according to your interest, then you will succeed in your life.

If your question is for MBBS or BDS, then it is not possible because bio is a compulsory subject and it is one of the criteria for the selection.

It depends on your interest. You can search the information for entrance examinations like JEE Mains. If you think, you can really do well, then you can go for it.
Best of luck.