Witnessing=Scary!!

I randomly woke up at midnight because God told me to be a witness to someone at school. At lunchtime God told me to sit beside her and share the gospel, it scared me so much I didn't do it. Lately my mom has been praying about witnessing to others and it was even the topic for our youth group, so clearly god wants me to do this. I thought one of my Christian friends that I usually eat lunch with would help me share the gospel but again and again that one empty seat that presents itself to me beside that girl everyday and I haven't taken it. I just don't want to do this alone. I read Acts7 about Stephen and how he shared the gospel in court even though he knew he was probably going to die and in the end he was stoned to death. I know that getting stoned to death isn't the same as (in a worst case scenario) getting embarrassed a lot but I just don't know how to start or what she is going to say. I have to do it today if I'm going to do it before Thanksgiving break, pray for me.