Have you ever had the thought that you're mistakes are so bad that God won't want to use you or answer your prayers? Take a minute and look through the kinds of people that God used.
We serve such a loving God that no matter what we do or have done he still wants to see us succeed. Do you realize that Jesus even called Judas to be one of His disciples even though he knew he would betray him? No matter what you've done come to God as you are and believe for that breakthrough in your life. As far as God is concerned your mistakes have already been forgiven. They were taken care of when Christ shed his blood and died on the cross.