Hi @lavaniya, the data preparation area only shows a preview of the data, not the entire data set, as this is an area for you to do things like check you have the right column names and data types, add calculated fields and join with other datasets.
If you want to visualise your data you would create an analysis, and there you can see all of your data, or filter it to show just the months you need.
I suggest you have a look at Guide to QuickSight Learning Resources which will guide you through from getting started to advanced topics.
Thanks for using the QuickSight Community, and happy learning!