“Uninviting” people to the wedding?

So I have an... odd situation. Several months ago, when I thought our wedding was going to be bigger than it is going to be, I sent out that WeddingWire link to have a few of our guests fill in their addresses so when it came time to send out invitations I’d be sure to have everyone’s. Well, over the past few months plans have changed from a local wedding to a very intimate destination wedding. As intimate as we can get. We’re only planning on have 20 guests (I would have preferred less but fiancé has a lot of family members he’s very close with and my step-family is very large). My mom has one of those guests that received a link to fill out her address in town right now. She’s no longer being invited, though I had yet to really explain that to anyone yet— until we have put a down payment on the venue. My mom said that her friend told her that “my family is very excited to attend the wedding” and my mom didn’t know what to do so she just kind of said “oh yeah it’s going to be fun!”.
Now neither of us know what to do and I’m panicking! I seriously wish I didn’t love to plan ahead so much because I wouldn’t have made this stupid mistake!