Dating anticipation, help?

I like this girl, and she likes me back. But a friend of mine was telling me that she is concerned about saying yes when i ask her out, because she is afraid of the relationship not working out and then we wouldn't be good friends anymore, like we are now. My friend told me to give her a few days to think things through, but this anticipation is close to driving me crazy. This would be my first real girlfriend. (my friend has been really good friends with this girl i like for years, and i am fully confident he isn't trying to screw me over. He has a girlfriend of his own.)

I know that for relationships to work, communication is absolutely necessary and each person needs to express their worries and problems or else tension will arise and the relationship could fall apart. I was planning on telling her that when, or if, i end up asking her out.

My question is: what should i do? How should i talk to her and hang around with her while she is still trying to make up her mind? How do i let her know our relationship, if there ends up being one, isn't there for all the wrong reasons (sex, sex, sex), but that i really want to get to know her better and take our friendship to the next level? What can i do to help her make up her mind?Thanks so much, i have a lot on my mind and i am getting stressed.