it puts pressure or places embarrassment on those who wish to stick to the original agreement
Only if those people decide to get upset about it.
Nobody can 'place' embarrassment on you – it's not a hat. It's a feeling you get when you place more importance on how you look or what other people think of you than you do on being yourself and doing what you want.
The people offering more food / fancier food are either coming from a place of care, wanting to give people as lovely an experience as they can, or a place of insecurity, where they worry so much about coming off as stingy that they overdo it.
Neither of those things are crimes, and neither of them twists anyone's arm unless they decide to twist it themselves. The refusal of some posters on here to take responsibility for their own lives is incredible (and I don't mean you by that, OP – your post was fairly mild compared to what's bubbling in the thread).
What next – don't wear your favourite jumper in case it makes other members of your book club insecure about their jumpers? Don't smile too widely at people in case other members of your book club don't have as much FACE as you?
Eat some food, or don't. Offer biscuits, or cheese, or make dinner. Talk about your book, go to bed, wake up, life goes on. What's the worst that will happen?
As PPs have said, send a message as a reminder, or just stick to the original agreement yourself and don't think anything more of it. Let people get on with doing their thing, and you do yours.
The unnecessary drama of some situations really does my head in....