Johnson said she didn't even realize the mistake until she got a message saying she had won $2 million in Saturday's drawing.
"It was definitely a shock," Johnson said. "When I got the message saying that I had won I thought, 'Well, I didn't even play tonight.'"
Johnson soon realized she had accidentally bought a ticket for Saturday's drawing and matched all five white balls, earning her a $1 million jackpot that became $2 million when the 2X multiplier ball was drawn.
Johnson said her plans for the winnings include a new house and a family vacation.
"The kids want to go to Disneyland," Johnson said. "We've never been and now we'll get to."