Try to remove yourself from the thought that they fancy you and think of them just like you would any other acquaintance you have. Just remember it's totally normal to feel awkward or nervous. For me, talking to someone who liked me freaked me out so badly, I became physically ill. Eventually, I got over it and everything turned out fine. Just be calm and chill out. It's just a person, don't sweat it.
I'm in transition of getting over my social anxiety and a few things I do to make myself less nervous is try not to think so much. The person you are when your alone should be brought with you everywhere you go. I'm not talking about the bad things, but try to bring that character with you everywhere and try to relax. Once you bring your true self into the public you will be more comfortable and havr more fun with life. Would you rather regret missing out on life or living it, while showing your true colors to the world?