I don't think it's wrong to speak of someone who is deeply devoted to God as a "saint"—someone who has a Christlike character and is committed to helping others in an exceptional way.
But your friend is right: In the Bible, every person who has truly given his or her life to Jesus Christ and is seeking to follow Him is called a saint. The word literally means "someone who is set apart"—and that is what we are if we know Christ. God has called us to be separate from this world and its sin, and He has set us apart for His service. Paul commended the Christians in Ephesus for "your faith in the Lord Jesus and your love for all the saints" (Ephesians 1:15)–by which he meant all of Christ's followers.
Does this mean we are perfect? No, of course not, not as long as we live in this world. And yet God still calls us saints, because we belong to Christ and all our sins have been forgiven because of His death and resurrection. And someday we will be saints in the fullest sense of the word, because Satan and sin will be conquered and we will be in God's presence forever.
Is this your hope? It can be, as you open your heart and life to Jesus Christ and trust Him alone for your salvation. Make your commitment to Christ, and then make it your goal to walk with Him and live as His saint the rest of your life.