Heaven is a perfect place, and we must be as perfect to enter, but scripture says that we have all sinned (Romans 3:23), and the wages of sin is death (Romans 6:23). It is wrong for us to judge ourselves against other human beings, because this gives us a false sense of security, and no religion or works can ever save a person, but when we judge ourselves next to the holiness of God Almighty, we all fall short of His perfection. Since we are all bankrupt, we cannot enter heaven by our own merits, because God will not accept the righteousnesses of humankind (Isaiah 64:6).
What we need is a mighty Saviour, and Jesus who is God in the flesh, came to earth to become a sin offering for us, dying a death that He didn’t deserve for all of mankind, so that we would not be punished eternally in hell.
Upon putting our faith in Christ’s death, burial, and resurrection, we are made righteous (positionally sanctified and sealed by the Holy Spirit of promise), never to perish for all eternity. We know that we are saved and going to heaven, because Jesus promised this, and Jesus is God who cannot lie.
These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God – 1 John 5:13