High gas consumption when using Manual, is this normal?

2015 Corolla S, purchased within this month. I was on a big empty road today and decided to try using Manual for the first time. At a full stop I shift to the Manual option (using the gearshift not paddles), press the sport button and take off at a reasonable speed. Not gunning the pedal all the way down, but still reasonably fast. I bring it up to about 80 and cruise there for a bit only to notice that my Remaining Mileage went from 199 to 195 in under a minute! I put it back on auto and turned off sport after that and it still proceeded to drop to 192 and then began to function as normal.
Basically, my issue is that I used 7 miles of gas in under 90 seconds. Is this normal, or am I driving manual incorrectly? Has anyone else had this issue? I tried it later on in non-sport mode and my remaining mileage still continued to plummet at an exponential rate - only 4 miles instead of 7 but the issue remains. Any input much appreciated!

It's just a computer that tracks previous records and extrapollates data. Calculate MPG at the end of the tank. The range is just an estimator.

If you're putting it in Sport and controlling the automatic it will use more gas when you keep the RPMs high.

As klinetime574 said. It's just an extrapolation. Any take off, sport or not, will kill that extrapolation. It take a whole tank to judge. And, of course, any "sportier" driving in those cars will affect MPG. Event 80 mph vs 70 mph makes a significant difference.