Your hunch is true for older cars where the fuel dosage would be in linear relation to angle of accelerator pedal - you floor it - you pump the richest mix, and even if a lot of it doesn't burn, or burns while the valves are open, you get maximum acceleration, like 100% power at 180% fuel usage.
New cars have this regulated by computer following calculations of engineers who built the car - while the pedal is to the floor, that doesn't mean the mix is at maximum richness. That just means the mix will be best for quickly accelerating without being wasteful.
If you do it yourself, you're trying to outsmart the computer. That never works very well - you don't let it calculate optimal curve to reaching the desired power by constantly changing the position of the pedal.
There's one more factor: constant overhead. Whether you stop in a jam or drive 100mph, or jump from one traffic light to another, there's always the energy that is constant over time used up by lights, electronics, friction of the gearbox and engine itself, all its pumps etc. The less amount of time elapsed during the trip the less of that you use up. If you drive at economy speed most of the time, you use less fuel.
