if I get 300 in neet can I eligible to apply examination in next year?

There is no cap on no.of attempts at NEET. You need to be 17 years as on December 31st of the year of admission. You need to complete your 12th, pass all subjects and secure a minimum aggregate of 50% in Physics, Chemistry and Biology. It is 50% for General Category, 45% for PWD and 40% for OBC,SC,ST. As long as you fulfil this criteria, you are eligible for appearing for NEET.