How long does it take to be grammatically fluent in Spanish as a native English speaker?

I studied abroad in a fully immersive Spanish program. I lived with a Spanish speaking family, I took Spanish classes. I normally had Bs in my classes. Today, I still watch TV in Spanish with English/Spanish subtitles. I can follow something without subtitles as well and understand the show/movie pretty well. I just won't get word-for-word. I listen to Spanish songs. I know a lot of vocabulary and not just basics but advanced vocabulary too like political terms or medical terms. But that said, my grammar is like a child's like maybe a 6 year old's. That really hurts my comprehension. The U.S foreign service estimates that for a learner that has done as much practice as me (over 3 months of immersion at 8 hours or more per day) that I should be fluent.

My language capabilities allow me to converse and be understood. But the grammar I have makes it impossible for me to work with the language professionally which is a goal of mine. It also sends a red alarm to native speakers that I don't fully grasp the language. It's normally things like using the wrong article, using the wrong gender for a word, at times using the wrong tense. I am trying to kick my learning into high gear so I can start fully using the language. But I am nervous because I've been working on the language for years and still haven't got it but I didn't really drill myself on the grammar. If I do dedicate myself to it and I'm definitely not starting from zero, how much time will it take?