Sir Can I get MBBS govt quota seat for 345 NEET cutoff in Tamil Nadu ?

You havent mentioned your Category. Neverthless in 2018, under State Quota, the cut offs for various Categories have been as follows:

General Category: 370
BC: 357
SC: 257
ST: 184


With 345 marks, you have a chance if you belong to SC, ST Categories. It is tad difficult if you belong to General, OBC Categories. Having said that, cut offs change every year and are dependant on various factors like no.of seats availble, no.of candidates appearing for the exam, top NEET score and difficulty of the exam. You can check the cut offs of each college at:

https://medicine.careers360.com/articles/neet-cutoff-tamil-nadu

You can also use our College Predictor services to check your options:
https://medicine.careers360.com/neet-college-predictor?utm_source=google-search&utm_medium=paid&utm_campaign=neet-clgpd