"Perfect", in the Greek, means "completed". It means to let God finish His work in you , and make you all you can be. This is a process, like in Rom. 12:2, "be transformed by the renewal of your mind". Your body follows your mind, but it takes some work, like practicing a musical instrument, or learning to type. God speaks to your spirit. Your mind needs to be renewed, so it can hear what your spirit is saying to your mind, that your spirit has heard from God. When your mind is renewed, it takes control of your body, and you learn to do it God's way. That's how it works, and it takes time.
To "repent" in Greek, is to change the direction of your thinking. Once you have decided to follow Jesus, you have done that. It remains in place, unless you choose to change back, and stop following Jesus.
If you read through Ps. 32, you will find there are lots of kinds of things we can call "sin". A sin of deliberate turning against God is different from imperfections that exist in you because you are human. Both are different from a sin of not understanding, for instance. All are sin, because they are less than you will be when God gets finished with you. God wants to heal them all. That is part of the work in you that you are to made complete (perfect) in. But they are different things. To get rid of the human imperfections, is what the Rom. 12:2 works best for; God shows you things and tells you what to work on. While God is finishing His work, it's great if you repent, because that's just praying for Him to keep doing it, and it helps you receive it better.
The reason people go to hell is they choose to not let God work on them (anymore, or not at all). The reason God tells you to avoid certain things, is because those things block the blessings He wants to give you. Even if you do them, He will still try to bless you, and that's why repenting helps, and trying to avoid them helps. That's what grace and forgiveness are for; they are His way of blessing you even when you still have sins, so you can get all the blessings. If you keep refusing God, and die that way, your soul will not be able to turn back to God after you resurrect at the end of the world. Then, it will hate being around God, and will end up burning itself in hell.
From the sound of your post,you are not refusing God at all. Satan loves to tempt people by scaring them that they're not good enough yet. He did it to me for many years when I was your age. That's why now I know better. Ignore what you are hearing in your head about all this, and focus on Jesus. If you want to follow Jesus, He will take care of all the rest of it. As long as you are trying to follow Him, you won't go to hell. And you will most probably outgrow these thoughts, as you mature in Him.
