Vettel claimed Red Bull's first win of the season in Bahrain last weekend but the German says that he is not happy with the current state of the team's car.
The 24-year-old said: "We're not as confident as we used to be.
"So small things can make a difference in qualifying and have a big impact on the race.
"I'm not entirely happy with where we are, but there's great potential in the car."
McLaren's Lewis Hamilton currently tops the driver's rankings.