We can be witnesses to others of Christ's salvation regardless of how great or terrible our backgrounds have been. With a tame past you can share about how the Lord has protected you throughout your life. With a less-than-stellar past you can be a witness of how thoroughly and positively the Lord has transformed you. Either way, after you've done your part in sharing your Good News, it's up to the people you've spoken with to respond.
It's been said that God has no grandchildren. Everyone who enters heaven is His son or daughter, not His grandchild or great-grandchild or niece or nephew. After you've brought someone to hear the words of the Savior, it is up to that person to choose to respond. The message Jesus offers is powerful. While the people of Sychar came to hear Him because of the evangelism of the Samaritan woman, they continued to listen and asked Him to stay with them because His message was one they could believe in. They came in response to one woman's witness and chose to stay in response to the Man Himself. While you can witness like the Samaritan woman, you can't force people to respond the way you'd like them to. Yet you can trust that the words of the Lord are powerful enough to have an impact on everyone who hears them.