Hi I'm 15 I don't know what to say,
Well anyway, I met a girl 2 months ago and I really loved her and we were just friends .
The problem now is that some guys in my class saw me talking to her and after that they told everyone that she's my girlfriend (I never said she was ffs), well the real problem is that her sister's boyfriend asked her if she's my girlfriend and she said no, and I think she's really mad now and she will never talk to me again I guess.
I'm thinking about writing a letter and telling her the truth but I'm afraid that she won't believe me:(
So please help and tell me what to do

Honestly, skip the letter part of it. Try to talk to her about it and just tell her you didn't say it and that it's just a rumor that got out of control. If she's worth it, she'll understand.

Just tell her, she'll understand. All of us girls know guys can be really immature and jump to conclusions all of the time (not all guys though, you seem like one of the good ones).

Well thanks girls, I'll try
And thanks again.