In Jesus’ conversation with Nicodemus, the Lord said, “No one has ever gone into heaven except the one who came from heaven—the Son of Man” (John 3:13).
In the immediate context of that statement, Jesus explained his uniqueness to Nicodemus. Only Jesus came from heaven to earth to explain spiritual matters to people. No human being has gone from earth to heaven to acquire that information and then returned to earth to share it.
Jesus is not saying that Christians do not enter heaven when their lives on earth come to an end. He is speaking about the source of divine revelation. That source is heaven, and Jesus came from heaven to tell people what they need to know and believe.