Saying whether or not you will get a seat in JEE Advanced 2019 based on 120 marks is very difficult to predict right now. Well there are a number of factors. First thing, of how much marks will this year JEE Advanced paper be. Second thing, you haven't mentioned your category(General/ OBC/ SC/ ST). Third thing, the difficulty level of the paper this year. Fourth thing, the number of students taking the exam. Fifth thing, number of seats available. Well, after combining all these factors, it is really unpredictable as of now. So, my suggestion would be that focus on scoring in JEE Advanced exam.
All the best!
JEE Main Sample Papers
JEE Main Previous Year Question Papers with Answer Key
Sorry to inform you but as per last year's cutoff for the general category you won't be able to make to it.
Jee Advanced examination is scheduled to be held on 27th May, and this year's cutoff will depend on it, therefore instead of predicting or expecting something you should rather prepare for the exam and then wait for the results.
All the best for your JEE Advanced!