If you can get 3v through a 3v motor and use a suitable gear box available at hobby shops then you should have a quick car.
How to make a solar panel car go faster.
If the car is powered though its wheels it may go faster than a car that is launched into the air by a bump.
Match your solar power output to a suitable motor.
Having a solar panel tilt on an angle can make it go slower so if it has solar panels try to put them on a level place on your car.
This will reduce rolling resistance.
Running surface run your car on a smooth hard surface.
Window sill for instance by running the car in an open area away from large buildings.
The car can be engineered to keep its wheels on the ground.
Course the car will run faster in a straight line than in a curve and faster on a flat course than up a gradient all other things being equal.