Is it OK to ask the girl if things are cool between us or what should I say?

i don't really know where things stand , we've know each other for a while now and I couldn't be more confused . one minute she seems interested and we talk , then the next she's in a bad mood . she works at a position where it be easy to talk to her so maybe I need to speak up ? but in a way that doesn't come across as too serious
Is it OK to ask the girl if things are cool between us or what should I say?
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