So you're afraid of rejection? I can understand, but what you should know is that life is full of rejection so you might as well get us to it now.
Regardless if I've known a girl for 5 years or 5 minutes, conversation is conversation. I talk about everything and it all starts with 1 question. Doesn't matter what that question is, as long as you get a response. It's always the same. I ask, she answers, I respond with my own experience to the subject and ask another question on the same subject or if she added a detail that stuck out, change to that detail and ask another question. The cycle then repeats. She'll eventually ask you a question. Instead of giving a one word response, answer with details, then ask her the same exact question, but worded differently. Cycle then repeats.
I honestly had to think about it before, but now it's so natural it weirds me out. I don't even think about it. Afterwards, I'm amazed because I wasn't always like this.
So, call her tonight. Not too early or late and have a conversation. Just remember your goal is to ask her out and not to really have a conversation. The coversation is just the ice breaker to your true intentions.