Hi Nazim,
As per the MicrosoftOffice2007 guideline, RibbonItems should get arranged based on available space in RibbonBar. This is indented behavior of RibbonBar layout. However, you could achieve your requirement by setting margin property for ButtonPanel explicitly.
For Instance,
In XAML:
TextBlock
Please let us know if you have any questions.
Thanks for choosing Syncfusion products.
Note:
It would be good if you post the Tools WPF related questions in the below link,
http://www.syncfusion.com/support/forums/tools-wpfRegards,
SudhaC.