Girl tells me shes into me but hasnt replied to facebook message?

We have really great time talking to each other lots of playful flirting till we were having a conversation and out of no where she didnt reply! (facebook message) she usually takes like 15 min. (we're all busy right?) but its been a few hours, and still no reply. Which makes me think why?! We actually were setting up a date for next week. So she is into me at least a little. I dont know i really like her, i felt different about her. What should i do?