Why did you put premium in a Fit? The engine will run happily on 87 octane.

Come to think of it, that engine may not have a knock sensor/programming to take advantage of hi-octane gas. If it isn't set up for that, you will actually get poorer performance and mileage than you would with 87. If it DOES have a knock sensor & appropriate code in the PCM, it will adjust timing to make use of it, but it'll still run fine on 87.