From your code I can see that each rotator item is 74px wide. If you want to see only whole items, then the rotator width must be a multiple of the item width. Also, when you set it, you need to take into account the width of the buttons on each side (20px each). So in your case if you want to show 7 items in the rotator, then its width should be 7*74+40 = 558px.
the Telerik team