Credit card balance transfer question?

What happens if you balance transfer, but you enter an amount that is greater than what is on the other credit card. I have a credit card that has pending refunds on it so I cant be absolutely sure how much my balance will be when the refunds come in, but I have to set up the transfer now because I leave for training for the military the 22nd of feb and a bal transfer takes at least 10 business days. If I somehow calculated too much (say i said transfer $2560, but there was only a bal of $2558 on the account) what would happen? would it still go through?