There is near enough 100 seats already reserved for this event, and I think the cap is 120, although Tom is finalising a few details with the venue at the moment.
If you want to play and don"t want to have to risk an alternates list on the day, I would strongly recommend using the reserve a seat facility on the homepage.
Entirely your decision though, and as Ian has stated, the fiver is non-refundable and you will still need to pay the £82.50 buyin at the venue on the day.