Oh, Erika, please take a deep breath. Remember that those who post online reviews often are posting because they're angry about something; unfortunately, folks often rush to post in order to blow off steam about a perceived slight, when they don't rush to post about something positive. There could be just as many or more happy parents at this preschool, but they just don't do things like post to online reviews.....
And as others note, the parents really aren't thinking about you. They don't even know who you are (yet). You are not on their radar. Unless there was some attendance list or roster of parents expected to attend this meeting you missed -- no one knows you intended to be there, so you weren't missed, so....they aren't brooding over how awful you were not to be there.
There will be other fundraisers. So sign up for those -- but not all of them, every time, because preschool is when parents learn how to say "No" to things or else they end up swamped. There will be other meetings. Go to some of them,, but not all of them. Same reason: Participate fully but don't become the "yes to everything" parent.
There seems to be a lot going on here: You work and seem to feel as if they'll brand you for that. You want friends for your kids and seem to fear that parents will hold you against your own kid and not let their kids be friendly with yours. I have to assume this is your first child in preschool. It's a lot of fun and it's important for socialization, but it's only preschool. When you hit elementary school you will have the same issues with how much you can participate as a parent, whether and for what to volunteer, etc. So now is a good time to learn to step back, pick and choose your participation, and focus on your kid's individual experience more than on the overall picture of parents' opinions, other kids' actions (which you cannot control), etc. You and your child will be fine. Best of all, since this is preschool and not regular school, if this place does turn out to be a poor fit, you can move your child, which doesn't happen in public elementary school.
So take it day by day and focus on your own child and his experience there, more than on your relations with the parents. You may find good friends among these parents or you may not and may never see them again. Either option is just fine!