I Am continuously getting 45 percentile in time cat mocks whats my chance of getting top b school or iim?

The cureent scenario predicts zero chances, you can only score well through practice, and with practice comes accuracy and speed. To achieve 99 percentile, you should be giving lot of mock exams. CAT is not about solvibg quantitatively but about qualitatively. When you give mock, make sure you do indepth root analysis of mistakes you make and check whether the approach you make is coreect, whether there is another approach which saves time. Make sure you jot down all such mistakes to not repeat them again. You need to check which is area of weakness and why are you scoring negative. Check how much time you devote on average. Then focus on those areas more, try to solve multiple problems on your weak areas through different books like Arun Sharma, Nishit Sinha, TIME Coaching material. Check whether the solutions set has different approach and does it save your time as well, in the exam hall you have to shortlist questions you're comfortable and confident with to save time and achieve accuracy.Give more mocks on it and eventually you'll optimize mistakes and achieve better accuracy ratio.

The chances are low. Remember its not about scoring good or poor in the mocks but how much time you put in analysing your mocks matters.
So where all you went wrong and which all are your weak areas and what are your strengths you should be getting this by giving mocks.

Aim at working on speed and accuracy of minimum 65 percent of the paper and hence you will be close to 90's and above.

Also practice previous year sample papers and attempt them like regularly so that in any case there is chance of question repetition then you have a hand over it.

Good Luck!