Okay... so if the price of bitcoin keeps going up, there's no way I can do the transaction, considering that it doesn't happen instantaneously, or what? Should I just keep cancelling and re-trying the transaction until it goes through?
if the price comes down, your bid will fill (if your bid is high enough that is). if you want your bitcoins right this instant, then yes, you would cancel your order and make a market buy (buy from the lowest seller). or you could place a higher bid.