"Depending on how many people sign-up, this tournament will be 64, 96, 128, or 256 man. The first 62.5% of the people who sign-up are guaranteed in while the remaining 37.5% will be randomly selected. If you do not get in, I will accept substitutes starting in round 1."
You fell in the category that was randomized and thus had a chance of not getting in. Feel free to sign up as a sub, just post in the thread if you want to do so.