Ofcourse you can score more than 300 in Biology neet by just reading NCERT line to line 

you should keep solving a lot of mcq questions related to a particular chapter so that you are aware of the trick questions they frame for confusion 

this will make you pretty confident .

All the best! 

Its difficult to predict that you will get 300 +. It all boiks down to how good you're wifh fundamental and how good your grasp advanced concepts. Majorly how well you performed in mock exams is great indicator of ezpected marks.

With persistent mock attempts and analysis of weak zones you can definitely score big.