To make it more clear on the pool site, use an asterisk after you team name if you are in the side pool.
For example: Vansmack*
There will be no adding an asterisk after kickoff Thursday, so add now.
If you have an asterisk by your name at Kickoff Thursday, you are on the hook for the extra $100.
In addition, you must be part of the $5 pool to join the $100 side pool. I thought this was clear but I've received a few PMs about it.
You do not have to participate in the $100 side pool if you only want to be in the $5 pool. If you don't join the $100 side pool but survive the longest, you only win the $5 pool, which could still be as much as $250.