Why you make mistakes
You know something is a mistake but you said it anyway. Does this make you feel uncomfortable?
You are an adult learning another language. As an adult, you are learning consciously using your ability to remember and apply what you know.
However, like other survival skills (walking, swimming, riding a bicycle), you learn language through repetition and through making mistakes. This is done unconsciously. Every time you make a mistake, you are learning what not to do.
In this way, your brain is organizing your new language. This means the mistakes you make, though uncomfortable, are essential to the process of becoming fluent.
So go ahead! Make mistakes. The beautiful thing about this process is the more mistakes you make, the more fluent you become.