“Double down” comes straight from blackjack: you double your bet after seeing...

https://idiominsider.com/talking-odds-at-work-the-risk-idioms-every-english-learner-gets-slightly-wrong/

“Double down” comes straight from blackjack: you double your bet after seeing your first two cards, doubling the risk for a bigger reward. Learners often misuse it to mean “do something twice