Hi,

You can definetly score 95 even if you haven't prepared 3-4 chapters. However, it all depends on your luck. If you leave important chapters out of which good amount of questions will come for sure, then you won't score good. If you leave chapters which contribute least to boards exam then you might.

It all depends on luck which you can't control, so I would say prepare all chapters. I won't prefer this strategy. You might be lucky, you might get good marks, but if you are unlucky, you might end up on the other side.