My friends bff is lying about me

For this post I will call myself R. My friend is K. Her bff is L and the guy everyone thinks I'm dating is S. We are all thirteen or twelve. I've been friends with K for years, since primary school. I'm not good with social interactions so she is one of my only friends and the friend I'm closest to. She's been friends with L for less than a year and spends a lot of time with her. I've recently became friends with S, a boy in my class. Most people find him annoying so him suddenly spending time with a girl was seen as strange ig? Most people think we are dating but we aren't. Im aro and he has a crush on someone at a different school. Im not too bothered by the speculation although it is annoying, but the problem is that L told many people that she spoke to me and I told her we are dating but I want to keep it a secret. She's never liked me but this is the first time she's done anything like this as far as I know. L knows a lot of people. People that could make my life miserable at that school if I say a word to her and I don't think K would get involved. K hates drama, to the point where it can be harmful to others. I know I maybe shouldn't be friends with K but it's difficult when I've known her for so long and it's not even her causing the problem. I know as long as this goes on people will continue to laugh at me and I have years left in this place. I'm quiet. I don't talk to people much. I don't have any friends other than S in my classes who can do anything about this. L is in all my classes so I can't get away from her. Even if L would listen to me, I'm an anxious introvert and there's no way I would be able to do it anyway. Is there anything I can do?