First off,it does not matter how long you have been a christ follower,Many people after hearing the word of God change their lifestyle and follow him and grow in faith. Chad germany ( a missionary) talked about how this one guy who heard his calling from God,then the next day ( not even saved for 1 week) said a pray for a guy who needed help and preached to him,guess what this guy who needed help heard the word of God and was healed!!!,So if you have followed God for 1 day or 4543 days you can still change and become a witness of God!Now for the next part...You do not always have to witness by preaching the gospel,but by showing Jesus love at any time you can,do it by being a great person,show people this is what my man Jesus did to me!,Being nervous in front of people is not anything new,My pastor was talking about how he is a quiet guy,and he is not normally a talkative person,but when he preaches he prays to God,and speaks up for what he believes in,asking God for help will help you out! You have not failed witnessing in my opinion until you stop trying completely!, You can try to evangelize somebody by preaching the word of God,Testimony's are a great thing to spread,but if your not mentioning Gods love,his greatness,how every knee will fall to the Lord,and say John 3:16,and how they need to change their lifes to serve the Alpha and Omega the begeniing and the end our LORD then how will they realize they must grow in their faith! Show them your love,show them how you care,what they may not realize even though your not preaching is hey this guy is great,make them want to be like you,without them even realizing you are actually showing God's love he has gave you and you gave him! Just grab a bible and read,there are people who have had the same problems,don't worry! just keep your faith strong and God will help you!!!God bless man!-Duke-