Okay so, I can understand how you feel, but I just want to let you know this might not be as bad as you think it is, long run. At nearly 40, one of the things that I've liked the best about growing up is how my perspective of my parents changed. Parents tend to show you a very censored, protected view of 'them' as you grow up. The first cracks can be interesting, funny, hurtful or even scary. This has obviously been a really emotional experience for you both. But your mother has just given you several compliments. She had a very painful, emotional, and private experience that - obviously - is still very raw for her (no thanks to her parents who obviously enjoy keeping it raw - jerks!). But after her initial shock she realized she had treated you unfairly and approached you to make amends (gee, if only her parents had done the same :/). The compliments in this is that she has to have immense trust in you to open up such a painful subject. She must see you as adult enough to cope with it. And she must love you enough to admit that her initial reaction was wrong, and approach you as one adult to another to talk it over.
This has been really painful experience for you all, but long-term, this kind of thing can make your relationship with your parents deeper and more meaningful than you could ever imagine it as a kid. My own mother and I, though we have some differences and there are some things she says that still drive me nuts, have a relationship a thousand times better than when I was a teenager. We've become friends as much as we are mother and daughter, and I'm reminded of that every time we have discussions where each of us can offer or request advice from the other, or just be there to sympathize and vent!
It might be awkward for a little while. It might help to have a visit with her one on one again where you just visit with each other. Invite her over for lunch, or to watch a movie together, or take her out for tea or a manicure or something if you can afford it. If she doesn't bring up the subject, just keep it to normal conversation. Friends, activities, school, work, whatever. If she brings up the subject you can listen, or discuss it, however you feel might be able to help your mom most. You can be honest with her. You can tell her how you feel. "I'm sorry for how I acted, it has been bothering me ever since how my actions affected you, I had no idea people like your parents existed." You can tell her you're grateful that she felt safe sharing this huge thing with you. If you really want to do her good, you can tell her how well she's succeeded as a parent. Hell, it's a pretty good indication of the success your mother has made of proving your parents wrong - from childhood on, she was aware there were bad people in the world, that some can be related to you, and that some can be bad while looking very good. Your parents took such good care of you you had no idea they existed. You did a normal thing late teens do - you questioned whether your parents' perspective was true, and you went to find out for yourself. Oops, you stepped in some dog shit. It happens! And you know, that's actually where I think (IMHO) they made a mistake that, fortunately, has led to no lasting harm. You are now at an age where your parents will be in the background, ready or able to swoop in if they see things going wrong. There are a lot of horrible people out there masquerading as good people. You can't live your life in fear of them, but you should be aware that they exist so that you can be on the lookout for warning signs. This has been your first experience. Now you know that nice words, a pretty garden, and regular financial contributions do not a good person make. You now have a little more armor than you had before all this began.
TL;DR: this has been a painful lesson for you, but don't let the pain distract you from the lessons. You are a good person with little experience. Your parents are good people with more experience, but they can still make mistakes - they just won't always be the mistakes you think they will be! And there are sneaky bad people in the world, but the good news is, no matter if they are related, offer you compensation, or have a nice house, if you find out they are bad, you can still say "I don't want this in my life" and walk away.