Welcome to the forum. My first couple of fill ups were around about that figure, but once I got used to the car the numbers started to go up. The dashboard display is reasonable up to a point, but only over a complete tankful. I find mine is about 2 - 3% optimistic. The best bet is to calculate the figure. Fill your tank, note the odometer reading, drive until tank is nearly empty, then fill tank back up. Calculate from litres to fill the tank and miles covered just what mpg you are getting. You can use a site like SpritMonitor
https://www.spritmonitor.de/en/ to calculate and store your numbers.
How you drive makes a huge difference to your mpg. Every time you use the brakes you have wasted petrol getting to that speed. Anticipation, and lifting off early, saves petrol. I also keep my tyre pressures up. I run at 35 psig, front and rear.
If you have just got the car, unless you know otherwise it is a fair bet that the rear plugs haven't been changed for a spell (i-DSi has 8 spark plugs
Dual
Spark
ignition).
Here's wishing you well with your new car. The Jazz is a great little machine.