This may be a dumb question, but did you press on the boost icon in the game? After you buy the boost (before or during the round,) it puts the boost icon in the lower right side of the board. Then you press on the boost's icon when you want to use it. If you have more than a few flames going, though, it would be hard to notice a single one going out! I'm sorry about your gold waste--it happens to me all the time. I've tried to train myself on timed levels to take my hands off the board a few seconds early if it's not looking promising, because I don't want to get robbed again. Though lately, I don't usually have enough to gold to steal anyway. I hate it when I finally win some challenge gold, only to have it accidentally spent on extra time...in a round I was nowhere near winning!
There are so many things wrong with the way they handle this problem. I've been posting about it for awhile, and started my own JM poll for a gold confirmation button, etc. But no one ever responds to these posts...makes me think they won't ever change it. There are too many people out there who keep buying the boosts and other stuff, so why would they change when they keep getting away with it? I'm guilty, too. I've bought extra time on a few levels that had me going crazy (I'd have done anything to get off them, lol!) Speaking of, I hope that you're done with 163. If not, I'm sending you good luck...we need to get you through that to cheer you up!