Hi Guys, I am new to dating etc. so I might have made some very obvious mistakes in this case. So, please feel free to be as brutally honest as you can and point out as many mistakes as possible.
Story--
I met this girl while walking home one day and we started talking. I was thinking of asking her out that day but couldn't find the courage. Anyway, the next time I met her, she asked asked me how do I like the city (I am new to city) and I said I haven't been around much and she should show me some time. She said yes and gave me her number herself, without even me asking for it.
Then, I added her on SPAM and from the profile pic its pretty clear that she has a boyfriend. I am ok with that, as I am new to city and would like to make some new friends. So, I waited for 2-3 days and sent her a message on SPAM with General chit-chat. this is a gist of conversation :-
Me - Hey, this is Ric, how are you
Her - Fine and you ? How was your day ?
Me - It was fine, getting used to the cold weather
Me - going to a concert right now
Her - its cool
her - i am doing my assignment
her - its cooler than a concert, believe me haha
*me - haha, may be i should give them a try

show them to me sometime
*I now think this was a really stupid comment
Then I got no reply from her for like one day. I sent another message the next day -
*me - hey, the weather is nice this weekend, lets hangout sometime
No reply yet !!
My question is 1) why give me number in the first place without even asking 2) why act like this afterwards.