No, Christ isn't like a medicine that works for some people but not for others. He is the universal remedy for sin for everyone who puts their trust in Him—including you. If you have sincerely turned from your sins and asked Christ to come into your life, you can be confident that He has done exactly that. And if you are unsure if you have done this, take that step of commitment right now.
How can you be confident God has forgiven you, and Christ has come to live within you by His Spirit? One reason is because this is what He has promised to do when we believe in Christ and give our lives to Him. The Bible says, "To all who received him, to those who believed in his name, he gave the right to become children of God" (John 1:12). The Bible also promises that because of Christ "we have redemption, the forgiveness of sins" (Colossians 1:14). These are God's promises to you.
At the same time, becoming a Christian isn't the end of our spiritual journey, but the beginning. God wants you to grow in your relationship with Him—and you do this by spending time with Him. Take time each day to be alone with God, reading His Word, the Bible, and praying. Become active also in a church where Christ is taught and lived. Don't let your spiritual life whither, but take steps now to strengthen your faith in Christ.