I am tensed about my NEET 2k18 I can get 300 or above marks but I want a government seat what should I do pls help me.......

Nothing to worry.. keep calm. Don't study anything new now,otherwise it will lead to anxiety and stress.. Only revise your notes and solve previous years question papers of neet ug.
Focus more towards ncert biology examples, figures, numeric values, scientists name etc etc.
Practise more and more.
If you have time left, try to read solved examples of ncert textbook of physics and chemistry..
Follow these , you will score 550+ marks in neet ug and would get a mbbs seat in government medical college through all india quota counselling.

Good luck. Prepare well..