The above images are the final products of the car. After I re-adjusted the chassis and wheel sizes to fit better, putting the car together was easy. However, I found that it was hard to get a rubber band around the back beam to have enough traction to be able to be wound back. After some experimentation, I managed to twist the rubber band so it would have enough friction to rotate around the back beam.
Although this did work, the back wheels would spin rapidly, but it would not propel the front wheels, rendering the mechanism useless. To fix this and give the wheels more traction, I added thicker, flatter, and smaller rubber bands to act as tires. In the end, although the car did not go as far in terms of distance as I envisioned, it was successful.
The mechanism that the car operates on is a rubber-band powered propulsion. In the chassis of the car, a small hook is placed on the front end of the car. The rubber band is looped into this hook, twisted sideways several times, and then looped through the beam connecting the two wheels. When one goes to rotate the wheels backwards or likewise wind the car up by pulling is backwards, the rubber band builds up elastic potential energy. When released, the movement of the rubber band snapping back to its original position causes the car beam to rotate, in turn moving the back wheels and the entire car.
Overall, I feel like my project was a success, but if I had more time or I was able to do the project again, I would first reiterate the design of the car so it would be easier to manipulate, and then I would make sure that the actual propulsion part of the car would work better. I could 3D-print more cohesive grips and hooks for the rubber band itself, and I could also change the wheel thickness so a rubber band functioning as a tire for grip would fit perfectly into the wheel.