You Can Do It! Just Realize You Can't.
I have to remind myself, these people in full-time ministry did not hone their skills overnight. It took lots of practice, and even some big failures and screw-ups, to get where they are. They've had to study, practice, and make mistakes. And (surprise!) they still get scared when they go out to witness. Even Paul got nervous when he preached. He told the Christians at Corinth "I came to you in weakness and fear, with much trembling" (1 Corinthians 2:3).
Yes, evangelism can be intmidating. But the only way to get better at it is to do it. You can't learn and grow by staying on the sidelines. Besides, fear and nervousness keep us humble, and humility is something God delights to use. Fear also keeps us praying and leaning on God for courage and strength. Besides, ultimately it is the Holy Spirit that does the converting. We are simply tools that God uses. So while training and study are important, remember that our true comptence comes not from ourselves but from God (2 Corinthians 3:5-6).
So rather than letting your fears hold you back, let them push you to move forward while leaning on Christ with all your might. You may be amazed at what God does through you.