I can't make up my mind about this girl.
Why are you unsure? Are you afraid of her?
I'm both afraid of her but also attracted to her
If you're attracted to her then you should let them know that. This will save both of you time and pain because it's better to know sooner rather than later whether someone is interested in you.
I'm not sure how to tell her sooner rather than later.
Well if you don't want her to think that you are leading her on, you have to hurry. Otherwise she might not care later on and will nothing to do with you.