Multiplying the bet amount by 7 times isn't bad at all. I thought about applying this strategy to other games, like roulette, betting on black or red, even and odd, 1 to 18–19 to 36, for example. Splitting it into 3 larger bets, approximately 33%, on each, instead of choosing one number, which pays more, but is also the most difficult.
It may not be feasible, but OP's strategy gave me some ideas…

Yes you are right but i use 8 bets daily.
I did also run AI over this and ai told me it's best possible way in terms of probability