I think, at this point, telling her how you feel is premature. You said you really didn't know her that well. Coming right out and saying you have a crush might scare her. Also, you're somewhat living in a fantasy of how you EXPECT her to be, not how she really MAY be. You may not like her at all once you make this reality.
That being said, I think you should ask her on a date. That will convey to her that you're more interested and also give you the opportunity to see if you really do like her better. You could say something to the effect, "I see you here all the time. Would you be interested in going out to dinner on Friday?" I know it's scarey but just think that this whole conversation will last less than 5 minutes. She'll either say no and maybe give an excuse or she'll be delighted and say yes. While you're at dinner, if you find out she is everything you expected her to be, you can slip in that you've been wanting to ask her for a long time but that you're shy. If it turns out she's not for you then she'll never need to know how you felt. Either way, you win.
A lot of men seem to end up in "friend status" by not being open. You need to search within yourself or maybe with the aid of a counselor, to find out just why you have this phobia about rejection. It isn't as tough as you're making it out to be in your mind. Your life won't end if someone says no. Chicks dig honesty.

When you take the chance of opening up the very worse thing that could happen is that the woman wouldn't feel the same as you. She may tell you she doesn't. I can gaurantee that she'll be flattered no matter how she feels about you. How can any of us help but be flattered when someone finds us attractive?
Give it a shot. Work up the courage to ask. Even if she says no, take it as practice. By keeping on, you'll eventually not let that special one slip away. Good luck.