Hello Sneha

You need not to worry for those extra chapters just focus on your studies and study hard. Whatever you studied in NCERT and previous board is sufficient . Bios exam is very easy one so that students can pass easily and prepare for their higher studies.

It's a good choice to go with this board. Actually my sister is also doing his intermediate from NIOS and at the same time he is preparing for Neet also.

Hope it helps good luck.