You can use the RadWizard Width
property to set the width of the control. It is visible from your screenshot
that the width is 0px, because it was set to 0px, either in the RadWizard markup or in the code behind.
Either way, you should check where the 0px value is set and change it to whatever value you need.
Also if you set the Width in %, e.g. Width="100%", the RadWizard's width would be responsive, depending on the window size. You could see this on the RadWizard mobile Overview demo
by resizing the browser window.