Hi there!
I don't do VCE but I'm sure the process is much the same
In general, you shouldn't force a line of best fit through the origin, even more so when it isn't a data point. Your line of best fit is the best fit for the data you actually have (excluding outliers) and should thus be roughly in the range of the first and last data points (unless they're also outliers). You also shouldn't force the line through the first and last data points (or any data point for that matter), unless your line of best fit actually passes through them
Extrapolation of the line shouldn't really be required or done unless a result off the graph in a future question is needed via extrapolation; in this case extend the graph with a dotted line to indicate extrapolation. ie. realistically, your line should start and end in the range of the first and last data points
Hope this helps