Well, change your board first, CBSE is way easier when it comes to Maths and English. Science in both the boards is almost same,so no worries there.
Get into a coaching centre, then you will know what to study, but don’t blindly follow them. Self study is most important.
Buy an NCERT biology and read it WORD BY WORD(yes, I mean it, refer to my previous answer given at the bottom)
You have to be very sincere.
And have fun, don’t stress yourself out, I wish someone would’ve said that to me.
And you don’t have to be a topper.
Do upvote.