Im Falling For my Best Friend?

I Love my bestfriend. She is the prettiest person ive ever seen. When i talk to her my heart races. I asked her out she said were so good friends and She said wouldnt it be a little weird? I need to know what to say to her. I want to explain to her to give me a chance and if we break up we go back to friends. I really need some help. Anyone help me? Its just so hard. Girl advice would be good too.