Did I blow my chance?

There is a girl I see about twice a week in class and I always catch her looking at me. There have been a few times where we both made eye contact and held it for a few seconds. The other day she smiled at me and I looked right back at her but didn't smile back. (I didn't even realize she had smiled until my friend told me after the fact). The last couple times I have seen her she doesn't seem to try to look at me anymore. Do I still have a shot?
Did I blow my chance?
Post Opinion