When my 2013 is full, it usually shows a gas range around 285-300. It will be less if your recent gas driving was inefficient, which it would be for short trips, for example. As in, you made most of your trip on battery and just used gas for the last couple of miles. The engine is inefficient while warming up. Your car is using about 26 mpg for estimating fuel range, which is very reasonable for short trips.
Also, don't worry too much about the octane. A number of owners use regular octane gas and don't notice any drop in mileage.
It is not a good idea to top off the gas tank of any car. It is possible to flood the evaporative emissions system equipment with fuel by doing that, which damages it.