How to prepare quantitative aptitude for CMAT exam , when I am poor in this section ? I am little confused and stressed as days are less .

Stress only adds to the pain and suffering but doesn't help in resolving the issue at hand. You need focus on the goal. Practise as much as previous papers as you can. QA can be categorised into Arithmetic, Algebra, Geometry and Advanced Mathematics. Practise chapter by chapter and develop mental calculations. Like practise more of basic summation, subtraction, fractions and tables. Numbers, Percentage, Profit and Loss, Simple and Compound Interest, Ratio, Proportionality, Time-Distance, Time-Work, Mixtures, Averages, Partnership, Permutation and Combinations, Probability, Set Theory, Progression and Series, Line, Angles, Triangles, Quadrilaterals, Polygon, Circles, Ares, Volume, Height and Distance, Coordinate Geometry, Basic Trigonometry are few important topics.
Because this section involves mathematics and takes most of your time, your focus should be on solving the problems efficiently in the beginning. Even if it takes time, practise upto perfection. Practise as many questions as you can in the conventional way. As and when you get a grip on the subject, you can go for short cuts. Memorise tables, square roots, cube roots, conversion from percent to fraction, etc. Solve sample papers on Mathematics. In the beginning, do not worry about the time it takes. As you practise, you will get the hang of the subject and it will be easier for you.