Taking a long time to talk to her doesn't look as bad as the eventual convoluted and tongue-tied mess that will be spewed out of your mouth because you are over-thinking things. Calm down and relax a little bit. It isn't that big of a deal. If anything, she will think that you were dense and didn't realize she liked you. Girls think that about guys all the time. Or she will think you are shy, which would then be balanced out by you going over to talk to her. Or she will think she was doing something wrong by not displaying her attraction to you enough, but again, your approaching her will counteract that.
Basically, it is not a big issue. Don't worry about it. Just talk to her and have a good time.
Good luck.
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