It's a newbie mistake but every now and then some people still fall for it. There are cases in which bets are doubled unbeknownst to the user especially if they clicked the "2x bet on loss" function. This still happens even though it's very clear what will happen if someone clicked on that. This doesn't seem to be similar in your case, although you still might have clicked on adding 1 whole ETH (does this function exist on your platform?) without you knowing consciously since you're in the heat of the moment.
Human mistakes happens despite being a pro or newbie. Sometimes gambling requires a lot of thinking and thinking of ways to win and strategy. Thus making you press unnecessary buttons.
I even tick the odds percentage unknowingly, and wonder why my bets keep losing. I think gambling sites should add another warning popup message, so that when a users mistakenly clicks "double bet button" a warning sign pops.