Desperate help required

It's too late by now to help the OP, but a few points need mentioning:

• If you self-describe as "running" the group, you have taken on some responsibility for preparing ahead of time; no advice any of us gives the OP is going to change that, or change that they are to some extent delinquent.
• Just how much responsibility depends primarily on the expectations you have set up among participants; are they in fact expecting you to have a rehearsed, structured activity to offer them at the meeting ?
• If expectations are low, pulling this kind of trick isn't so bad; it can help place the group in a reflective frame of mind, and at the very least pave the way for discussions of how "meta" it's rational to go.
• Irrespective of expectations, the above can be much more than a "trick" - the book Software for Your Head that I mentioned elsewhere arose from several iterations of essentially the above exercise. However, careful preparation, well ahead of time, would still be valuable if you picked that option.