Cancelling the order is not good advice as your order of placement will change. Just call them tell them what has happened and they will amend it and you'll stay in the same order as previous.
I did it with ETrade and am still in the same placement order.
instocks suggestion is to purge the order (cancel) and place a new order not the smartest way.
No offence to you instocks.
Just trying to give better advise.
