What is the possibility of getting an M.Sc. in physics seat in Central University of Rajasthan, Karnataka and Punjab, if I am securing 33 marks in the CUCET 2018?

The chances are less but it does not mean that you cannot get admission. Securing a seat in CURAJ with 33 marks is difficult but you can easily get that in Central University of Punjab (CUPB). 

During the first, second and third rounds of counseling, you may or may not get seats but after that the university conducts an open counseling and spot admission. 

Every year, seats remain vacant in almost each and every course in CUPB. You may get a seat in the third round of counseling or after that in open counseling.