With 345 marks in NEET, securing admission to a private medical college for MBBS is possible, but your chances will depend on several factors:

1. Category : If you're in a reserved category, you may have a better chance compared to the general category due to category-based reservations. You should check the specific cutoffs for your category.
   
   

2. State and College : The cutoff for private medical colleges varies by state and college. In states with a higher number of private medical colleges, the cutoffs are usually lower than in more competitive states.
   
   

3. Fees : Private colleges typically have higher fees compared to government colleges. The availability of a seat in a private medical college depends on the number of seats and the cutoffs for that particular year.

You will likely have a better chance in private medical colleges in less competitive regions, but it's important to keep an eye on the counseling rounds and cutoff trends for private medical institutions in your state.

For accurate and updated information, please refer to the official NEET counseling website or private medical colleges' official portals for admission details.