Achieve a big win and select the double your winnings option. Select a chest to see if your number wins. If it does, great but if it doesn’t, immediately hit the home button. Close the game out completely (iPhone by pressing home button twice quickly then pressing the game icon and holding it. It will shake the icons and an x will come up on it. Press the x to close). If you close out the game fast enough, you won’t lose the coins you received from the initial win.