Have you tried setting rangePaddingHigh, and rangePaddingLow on your x axis? Setting both of these properties should add a gap of fixed size at the start and end of your axis. The following code snippet demonstrates how to set both of these properties to 1:
xAxis.rangePaddingHigh = @1;
xAxis.rangePaddingLow = @1;
ForSchartCategoryAxis The padding is based on the number of elements in the axis. So if you graphs has two elements in it (as shown in your screenshot) this should add an extra elements width at either end of your axis and give you your desired look.