What does she mean by this?

I'm a pretty shy and quiet person and I keep to myself. But today I asked out a girl I've really liked and I thought there was mutual interest, and what she said was no, and she then added she didn't know when I was having a good or bad day and she left it at that but then just walked off.
We are doing a summer class and she goes to school with me over the past year.
What does she mean by this?
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