Does being a member of a church mean I’m a Christian?
No. Turning from your sin and trusting in Christ makes you a Christian, not being a member of a church.
However, church membership is meant to be a church’s corporate affirmation of your profession of faith in Christ. Membership is supposed to be the church saying, “We’ve looked at your life. We’ve heard your testimony and your explanation of the gospel. You look like a Christian to us, so we’re happy to affirm you as a Christian, welcome you as a brother in Christ, and care for you and watch over you.”
So, while church membership is no guarantee that a person is a Christian, it should offer genuine Christians some assurance of their salvation.