Very nice first road trip!
What he said. Put a few tanks through it and keep track of your fill-ups. After 4-5 tanks you can look at your DIC indicated mileage for each tank and then compare that to you actual calculated mileage based on fill data and odometer readings. You'll come up with a correction factor that you can use to better estimate your mileage.
I correct mine at -7%, others seem to vary between about 5-10%. Even so, my correction factor isn't exactly the same each time, so the only way to be sure is to average it out over full tanks. With the Eco and it's early fuel tank cap-off (which gives it an artificially limited 12.9 gallon capacity), filling can be a little inconsistent as well depending on the flow rate of the specific pump you're at and how level the car is sitting. That's why I suggest working out your correction factor over a few tanks.
There are lots of fuel tracking methods you can pick from as well; Fuelly (most popular), Ecomodder (see my sig), and many more I'm not aware of as well as countless smartphone apps. I use a smartphone app to record my data at the pump and then update my on line trackers at home on the PC. This saves me from having to keep track of paper reciepts.
Welcome to the forum, and good luck with your mileage!