How can you tell if a girl likes you?

Well theres this girl i met last week she just came up to me and said hi and i said hi back, i dont even know her she was in my 5th period last year but i got switched out very soon, we didnt talk till later that week i saw a friend of mine i havent seen in a long time and then she came in the conversation saying hi again this time asking me my name before i said anything she told me her name then she shook my hand saying nice to meet you then i said my name then the three of us were talking then she asks me "do you have a girlfriend?" i was like "nah" then she giggled and said "dont lie" what do you think? Does she like me? I think i mightve messed it up though because my friend talked about and incident i had with another girl ( i got a handjob from a girl i thought was single) she knows her but not sure if she knows shes a slut (she did say she was ugly though). But She didnt seem disgusted or anything ( it didnt seem like it i could be wrong) the three of us kept talking . Do u guys think i messed up?