If you try to reduce the width of the bar chart, most probably you'll face problems with the long values on data points.
What you can do, is go to Number tab of your chart properties, add Symbol (£, $, ...) and then Thousand and Million symbols (K£ and M£ for example) and select Fixed to 2 decimals as number format.
Then you'll see much shorter numbers as values on data points so you can safely reduce the size of your bar chart.
I hope this helps
Let me know if you need anything else