Solution 1:
Make Report Property ConsumeContainerWhiteSpace=True.
Solution 2:
Make Sure Your Report Body Must be Small than The report size.
The Calculation is simple just like,
Report Body Size<=Page Size+margin Size.
Example: Your Report Body size 8.25 INch.
Your Page Size is 8.27 Inch.(for portrait)
so the equation is 8.25<8.27 where all the margins Are 0.