It's really hard to get free seat with 300 marks because usually for the merit list you need to score above 500 still after this also they charge minimum fees for the course with the 300 marks you can get seats in private colleges if you are looking for any specific college you need to be active in their official website and regularly check the updates

With 300 marks in neet I hardly possible to get seat in mbbs even in govt college scores needed is 500+ so better try for private institutions which demand to pay more fees and if possible try again giving neet and try score more marks more than 500+ or look for any allied health courses