Three years after California launched a savings program to help children pay for college, most families still haven’t claimed the money — and many don’t even know it’s there. The more than $2 billion program is designed to close the college access gap, especially for low-income families. But many Californians are missing out simply because they haven’t heard of it, said Cassandra DiBenedetto, executive director of the state-run ScholarShare Investment Board, which oversees the program. “Our biggest challenge is also…