God is calling, but I am full of self doubt

Just recently, I was called on by God through another believer to stand up and TEACH a workshop. I've never been able to stand up and speak in front of more than 2 people without breaking down and crying. Or, even teach anyone other than my children. I get nervous and forget everything I know. I've been stressed and crying the last few days knowing I have to do this in 2 days. I know if I don't, I am disobeying Gods will for my life and will never prosper myself and my family like I believe he wants to! Does anyone have any scriptures or advice that actually helped this defeat this spirit of fear?