I am not using any panel or form. That white space is the background of datagridview.
If you don't want to allow user to scroll down the grid lower than the last row, you have to implement custom painting.
Please, read this: How to: Customize the Appearance of Rows in the Windows Forms DataGridView Control | Microsoft Docs
i'd not recommend to change default behaviour of datagridview painting unless you really need this. I'd change the background color if this "white space" is really annoying you.