So the MPG has a couple of ways of been shown.
You have the 'trip' counters 1&2, these allow you to measure your MPG over 2 waypoints. The other, is the 'live' one, and yes 118 will be correct, but watch as it drops out to say 15mpg accelerating hard, it will balance out! You often will see 999 mpg too.
Have a go at re-setting one of the trip counters, see how you get on.
ECO mode, there is a little switch by the right hand side that allows you to disable eco mode until you next switch off the ignition, it is possible you hit that. Also ECO mode doesn't like when its cold, it is
IIRC effectively a heat storage device, that has compressed hot air inside it, to instantly restart the engine. The car won't go into eco mode if you are using a lot of electricty, say you have it on quick de-frost mode or similar.
You can observe this by when you release the clutch (gear in nuetural) it will flash green ECO in the rev counter area. If it is flashing, it's detected that you want it to go to eco, but it can't because of either too much power drawn, or too colder engine or the battery is a bit flat etc.