In order to display a range of values along an axis set the AutoScale
first and then set the axis MaxValue, MinValue and the Step. More about axes can be found here
You could also use the AddRange method like this:
radChart.PlotArea.XAxis.AutoScale = false;
radChart.PlotArea.XAxis.AddRange(0, 100, 50);
Regarding your issue with not showing all the rows, I've created and attached a sample project using a DataTable with columns and rows similar to those you've described. Could you reproduce your issue there, so we can find what is causing it.
the Telerik team