Yeah, at 13, this is a fight you’re going to have to have.
First, I would give her a chance to come clean, asking about her plans at the weekend. Then I’d tell her I know the truth and that there are two issues with that, first is that she lied and second , that you don’t know this boy(and neither does she?!?, it’s not clear how they met or if they actually met before). I’d remind her of the dangers and be very clear about them and why you are concerned. I’d remind her that you are her mother and you have a responsibility to keep her safe. That you trust her (or at least did until now), but you don’t trust other people, especially someone you have never met.
Then the biggie , she’s grounded this weekend for lying. Make it clear that If she had been honest, you could’ve worked with her to find a compromise. Tell her she can meet the boy another time , or even better he can come over to the house (watch a movie , have dinner etc.) so you can meet him , but she needs to be honest about who he is and how she knows him. If she is adamant she wants to meet him in town, you will drive her there , meet him and they can have a drink/something to eat while you do some shopping and you’ll be picking her up to take her back home. If she doesn’t agree, it doesn’t happen.
At this age , these are the fights worth having. She can hate you all she wants, scream,shout ,swear whatever. You have to parent her.