RadListView has three properties for controlling the size of its items:
AllowArbitraryItemWidth - allows items to be auto-sized according to their content horizontally. AllowArbitraryItemHeight - allows items to be auto-sized according to their content vertically. ItemSize - sets the size constraint for all items in case any of the previous properties is false.
In your case, you can either increase the ItemSize so that the values you want to display fit within the specified size, or set both AllowArbitraryItemWidth and AllowArbitraryItemHeight to true, which will allow your items to be auto-sized in both directions. In both cases, the horizontal scrollbar will display and will allow you to scroll through your items' content.