Does an xray show widening if blood vessels accurately?

Not usually: Plain x-ray is not a usual modality to evaluate blood vessels. If by "widening" you mean dilatation or aneurysm, ultrasound is the most common diagnostic tool to start with. However, depending on location of the vessel ct or MRI may be reasonable starting points. Ct does use xray. Angiography is a diagnostic tool I use when treating blood vessel disease and is very good at evaluating as well.

No: An x-ray does not give information on blood vessels. Sometimes the vessel calcifies and we get a rough look, but if you want to look at blood vessels (depending on location), you would use other types of imaging (ultrasound, ct, mri, angiogram).