I have a curve of time vs. amplitude. I have need to show the xBottom scale from time 0 to 600 seconds, but I only have 481 data points. How can I get the scale to be the full range of 600 seconds, but only use 481 points to fill the entire graph from left to right?

Here's the code:

double* xVal;
double* yVal; //this gets set somewhere else, it is of the same size
const int Size = 481;
double xval[Size];

for(int i=0; i<Size; i++)
{
xval[i] = i;
}
xVal=xval;

m_plotDomain->setAxisScaleDraw(QwtPlot::xBottom,new TimeScaleDraw(gCondenser->m_pageStart.time()));
m_plotDomain->setAxisScale(QwtPlot::xBottom,0,600);
m_plotDomain->m_arrayData = new QwtArrayData(xVal,yVal,Size);
m_plotDomain->m_curve->setStyle(QwtPlotCurve::Lines);
m_plotDomain->m_curve->setData(*m_plotDomain->m_arrayData);
m_plotDomain->m_curve->plot();