"I'm truly the happiest I've ever been," says the Malcolm in the Middle star

Malcolm in the Middle star Frankie Muniz has traded in acting on the small screen for speeding around a racetrack.

“I never really wanted to get out of acting, but now I’m a professional racecar driver,” the 21-year-old tells PEOPLE. “Seriously, ask any actor if they’d rather be a professional racecar driver or an actor.”

Muniz drives in the Champ Car World Series and will participate in Sunday’s Las Vegas Grand Prix, a 2.44 mile race around the city’s downtown, which will be televised on NBC.

“I’m truly the happiest I’ve ever been in my life,” he said at a gala event Thursday to promote the race.

“I like the fact that I basically control my destiny with how much effort I put into working out, testing and training and becoming a race car drive,” he explained.

“As an actor, it’s all what people think of you. You can do your best job possible but if someone says it sucks, it sucks. Whereas here, if I’m good, it will show.”

Having spent only 40 days at home in the last year, Muniz admits that his relationship with fiancée Jamie Gandy, to whom he got engaged in 2005, has taken a hit – but he’s confident things will work out.

“We’re still together, but we kind of took a step back for the racing purposes,” he said. “She’s doing her own thing and she wants to have her own life and not just follow me around the world. … I’m so happy when I’m with her, so we’ll see.”