Call the store where you have it reserved.
Had a very charming conversation with Ellie from the Exeter store where mine is reserved who assured me through looking at her system that my name is on a list and 1 will be available on the day. However, she did say that I should bring in my conformation e-mail and other documentation for the contract purposes.
What she did mention which was a very valid point and certainly one I never took into consideration, is the amount of time needed with each customer upgrading or starting a new contract.
She said it takes about half an hour to process each contract customer, so should the store anyone is collecting reserved phones from have a high volume of contract customers queuing, don't expect the queues to be moving that quickly.