My friend is really mad at me for a stupid reason. Help?

So my friend, (let’s call her Susan), really likes this one guy,(let’s call him Paul). Paul happens to live really close to where I live, so I usually walk home from school with him everyday. He’s a really cool guy, and just the sort of person that a girl can really be friends with. Susan was fine with all that until he asked me out the other day. I said no and made the boundaries clear, and Paul just accepted it and nothing has changed between us. Unfortunatly, I was stupid enough to mention it to a friend who told Susan. Now she says she isn’t mad but she is ignoring me and won’t look me in the eye, along with many other things. To top everything off, some of Susan’s friends have told a ton of people that I did say yes and only to irritate Susan! How can I address Susan and my fellow classmates?