Exactly as Pine says. Expansion.
If you have a 5L petrol can for garden equipment in the car, it doesn't half balloon/crumple up depending on the temperature.
I've filled the Jazz up to 1st click at over 40 litres. The low level light is nominally 7.2L in the manual,but this figure is noted in a service bulletin as +/- 2L, so it could be 9 or 5.
Do you need to force so much in?