Yes, you are missing something; you're missing the great truth that God loves us and accepts us just as we are!
After all, if we had to wait until we measured up to God's standard before we could be saved, then none of us could ever be saved -- because God's standard is nothing less than perfection. Furthermore, if we could somehow measure up to His standard and therefore make it into Heaven on our own, then we wouldn't need Christ to save us. But we do need Christ -- because He came into the world for one reason: to save us from our sins. The Bible says, "But God demonstrates his own love for us in this: While we were still sinners, Christ died for us" (Romans 5:8).
Think for a moment about some of Jesus' disciples. Did Peter "measure up" to God's standard? No, he denied Christ after His arrest -- not once, but three times. And yet Jesus forgave him, and God greatly used him to win thousands to Christ. Or think of Paul. Did he have to "measure up" to God's standard before Jesus would accept him? Not at all; he persecuted Christians, and yet Jesus forgave him and welcomed him just as he was -- and you and I are here today because of Paul's faithfulness.
Don't let anything -- including your fears that you aren't "good enough" -- keep you from Christ. He loves you so much that He gave His life for you, and He is willing to welcome you just as you are.