can i get 450+ marks in NEET 2020 if i start preparing now?

You have around 4 months in your hand for preparing for NEET 2020. Devote your time only in preparation. Keep yourself aside from any type of attractions. Making a smart and pragmatic study schedule is the first step. NCERTs are considered as the best books for NEET Preparation. You can also study another books like H C Verma and D C Pandey for Physics, ABC of Chemistry for Classes 11 and 12 by Modern, J D Lee for Chemistry, Biology Vol 1 and Vol 2 by Trueman, Objective biology by Dinesh etc. Solving previous years' papers will help you to get idea about what type of questions usually come. Give mock tests as many as possible.
http://medicine.careers360.com/articles/neet-preparation-tips
It's not too difficult, if you study properly, focusing on your target, you can achieve the same.