Should I be worried ?

I went out tonight for a drive, started my car to let the engine warm up, and at the same time the battery charge builds up. My fuel rating is showing 15.0/100, I get it , I have not moved yet, but I start driving on the city streets making my way out of town, the rating has changed to 8.4/100 at about 6 blocks away from home, I get out of the city doing a average speed of 70 kph, my rating is now at 4.6/100 I'm happy because the rating did not get stuck on 4.7/100. I come up to a nice windy road posted at max 50 kph, I put the car on cruise after a short couple of minutes my rating changes now to 3.8/100 mostly because I have the cruise on. But now I leave this area to turn on a different hwy to come back home, speed limit is posted at 100 kph. I have my cruise on 80 kph all the way my rating has changed now to 3.6/100. Now I'm back in the city driving 50 kph. And just getting home and my final fuel consumption rating is now on display at 3.5/100. Temp outside is 6 degrees Celsius. I drove about 65 km total distance just over a full hour and ten minutes. This is a perfect example of what I'm talking about , since most of my driving was very long consistent speeds the ratings did not change often, .my point before was I have times while driving the rating will get to 4.7/100 and stay on that number for the full drive, no matter what my speed is ,100 kph or even down to 50 kph in the city at 30 degrees Celsius summer time. Until or unless I pull over and turn the car off and back on .to reset that stuck rating number.which usually works. One day I had to turn off and restart the car 5 times to finally get my fuel rating below 4 into the 3.3/100 and without changing my driving speeds or habits.
I have had times coming home from work with a still warm engine, got back into the car and drove 5 blocks to the grocery store without paying much attention to the ratings yet stop the car and noticed that I got a rating of 2.7/100, now explain that when sometimes I need to drive a full half hour in the city to get into the low 3's/100 ratings. Yes with a warm engine you can achieve good numbers. I'm strictly talking about a fuel rating over /100 that constantly changes based on your style of driving light foot or heavy foot on the gas while driving or starting. My original complaint is that all my plms started after my first oil change, I think the dealer hooked up to my computer and it screwed with something, I have since now already had my second oil change ,my car is 6 months old and I have almost 18,000 kms on my odometer.having my current fuel rating to show up accurately has been a hit or miss everytime I get in my car. It's hard to show someone when it works fine, then times it gets stuck on 4.7/100 I have given up trying to convince people that my car has this little glitch. When I know so well how to handle this car at its most fuel effient ways, my front grill is covered with foam piping, zip tied on, my tires are at 42 lbs for less resistance, I try to keep my green power band at the half mark all the time, I can now reach a constant 62 kph on ev, until the power level drops, I use my engine breaking in traffic so not to have to come to full stops and help keep momentum.every fuel refill I work out my mileage based on litres put in and total distance travelled , I average every fill at about 63-65 mpg. Yes I convert my fill ups .and I reset both my trips until next fill up, and I also input the price of fuel into the dash computer. I do not watch the stupid bar graphs changing all the time especially when it does not show precise numbers like the current fuel consumption rating shows like 3.8- or 3.7 or 3.6 the graph will not say exactly but those small fractions are as simple as dropping your cruise control by one kilometer speed, that active fuel consumption rating changes or I should say updates every ten seconds no matter how fast you go or how long you drive. Hello does anyone understand how their cars work ?