We do not have the self-contained ability to be perfect. Does our agency give us the ability to be perfect? No. It might technically give us the option, but it does not give us the power nor the knowledge.
Could Peter have chosen not to doubt when he started to sink? Technically yes, but he didn’t. And I think he really couldn’t have. He is human. He is weak. His lack of strength made him lack the drive to choose perfect faith in that moment.
Christ, when he was born, was not complete nor perfect. But, he lacked all of our inherent weaknesses and had within him every possible strength. At least the strength of perfectly relying on God. And in that strength, he only made right choices.
You will make mistakes. Remember that because you are weak, a human, and NOT a God, mistakes are inevitable. As you rely on God and continue to strive to make better choices, you will be more able to avoid mistakes. But until you are perfect they will always be there. Not because you are wicked and malicious, but because you are human. There are moments when your agency will not be enough to overcome your frailty and you will do wrong.
You can build up strength now through prayer and effort to avoid some future mistakes, but the best strategy is to not let past mistakes bother you, instead use your energy to repair the damage and to prevent future errors.
My son, perhaps technically, has the right to choose to speak perfectly, but not the ability nor the knowledge. He has no external restriction placed upon him, only internal.
We can’t just choose to be perfect. We can choose to rely on god, and then his knowledge and power will help us to slowly go through our metamorphosis. To use this cocoon of life and hardship, and to emerge as something greater.