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.
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.
You can make it a streamlined shape like a racecar.
Running surface run your car on a smooth hard surface.
This will reduce rolling resistance.
Match your solar power output to a suitable motor.
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.
Window sill for instance by running the car in an open area away from large buildings.