New 2015 Honda Civic LX - steep drop in Gas Tank bars in three days?

New 2015 Honda Civic LX - steep drop in Gas Tank bars in three days?!

Added (1). I bought my 2015 Honda Civic LX 3 days ago, and have only driven it 40 miles so far. When I stepped out of my car last night, it showed a full gas tank. When I stepped into the car today morning, it showed 2 bars less in the gas tank. What's wrong?!

Either you had the econo button on when it got better mpg, air conditioning cause mpg loss, driving habits cause mpg loss… It's probably one of those since it's a 2015 and its not exhibiting any other symptoms