and for future references don't say you'll start dating some one and then change your mind so quick.

She plucked up courage to ask you, so obviously she had strong feelings for you, which you intensified by saying yes to her proposition.
Now you went and changed your mind so suddenly, and you don't see it as your own fault for her current actions?
You should at least man up and try it, you seemingly got yourself into this mess, the least you could do is try.