Last year I seemed to recall that you could book your room starting on Wednesday. Am I not remembering that correctly? If I am then this year seem quite different. Starting on Wednesday didn't seem to be an option and booking outside of the block is a tremendously more expensive thing ($500+ for Wednesday night).
It's as if GenCon made a deal with the hotel conglomerate to reduce the span of the block knowing that many many people still needed a Wednesday room.
No? I booked Tue-Sun in block. Were you looking at a specific hotel? Or perhaps weren't looking at the right month, since the Wed is in July and not August?
I booked Home2 Suites Downtown for Wednesday through Sunday, and got the in-block rate for all four nights.
This was discussed after Gen Con staff had the same problem while demonstrating the housing process!
The dates show up as two calendars, one for July and one for August. August is centered just where you expect a calendar to be. July is off to the left.
Wednesday is visible but grayed out on the August calendar because it is July 31.
If you made a reservation from Thursday, try modifying it. You won't lose your existing reservation until you confirm a new one.
(If you had the problem while actually looking at a room type, then they've sold out of Wednesday rooms.)