Jesus did not mean to imply we are already in heaven. The idea He was trying to get across to the people was that the kingdom of heaven was near. In other words, the Day of judgment is closer to you than you think, and you need to get right with God. Time is running out. Stop playing games. Repent.
Matthew 7:21 NKJV: "Not everyone who says to Me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven."
Notice how Jesus says, "shall enter the kingdom of heaven". This tells us that this event is yet future, that we aren't there yet. He also says the Father is "in heaven". In other words, heaven is a real place where God is, and if we want to be there with Him, then we must do His will.
Matthew 7:22-23 NKJV "Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?' And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'"
Jesus is making it clear that not all who say they are His followers are speaking the truth. In other words, there are fakes out there. They look religious, and use the name of Jesus; yet, they don't have a relationship with Him.
Jesus also speaks of a coming day when this will happen. Which day is He referring to? The day of the harvest when the wheat will be separated from the tares—the Day of judgment.
Matthew 13:30 NKJV "Let both grow together until the harvest, and at the time of harvest I will say to the reapers, "First gather together the tares and bind them in bundles to burn them, but gather the wheat into my barn."
1 Thessalonians 4:16-17 NKJV "For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord."
John 5:28-29 NKJV "Do not marvel at this; for the hour is coming in which all who are in the graves will hear His voice and come forth— those who have done good, to the resurrection of life, and those who have done evil, to the resurrection of condemnation."
This has not yet happened; therefore, we are not in heaven. But we should prepare our hearts for heaven by getting right with God; for the day of God's wrath is drawing nearer day by day.