Sorry to say you can't expect to get it for free if it is obviously not the correct price. If it goes through then great, but if they pick it up and try and charge the correc t price then you would have to pay that.
There is case law relating to this scenario, and the fact that it is obvious this is the wrong price will not help you.
Same with shops, you can't force them to honour a wrong price if it is a mistake. You can try and they might agree, but they don't have to. Common misconception.