Continuity mistake: When the Ferrari stops in the petrol station and the young lady catches the Italian driver's eye, in the first shot he's slapping his face, then in the next shot he is wearing sun glasses which he didn't have before.
Factual error: As everyone races through Illinois, notice the very large mountains. Illinois is a very flat state.
Continuity mistake: At the beginning when the police car is leaving the Gumball start base it crashes with the undercover cop car. The left rear panel gets damaged and the trunk pops open. The next time you see the police car there is no damage.
Continuity mistake: Whilst the Cobra is in traffic, before race through the LA River, the front of the car is damaged and one of the spot lights has been bent round, yet when you see the car again as it enters the river, the front is not damaged.
Plot hole: When the Ferrari stops for fuel at night, Franco decides to spend the night with the girl in the Mercedes. His partner protests, then abandons Franco to continue the race. The next morning, the girl drives Franco to meet up with the Ferrari again. This is a coast-to-coast race, planned out in detail by each crew long before to take the shortest course at the highest speeds possible. First car to L.A. wins. It isn't possible for the Mercedes to just 'catch up' to the Ferrari the next morning unless the Ferrari was taking a wildly wandering course or driving incredibly slow for hours.