You are not alone…
Incidentally, @vero’s words merely echo what many folk think (French and English)… so it’s nothing “personal” just, in many cases, a misconception.
None of us has the same capabilities… some will absorb all the nuances and grammar… some of us float on the edges… no matter how hard we try.
I can talk the hindleg off a donkey, in French (and English ) , on any topic under the sun.
I use my own technique of words/phrases for those occasions when I don’t know the correct words/phrases and/or don’t understand what is being said.
This has never met with an adverse reaction from French folk, rather an appreciation of my efforts.
But… sadly, that is not how it works in an exam.
and… exam jitters have bugged me since my schooldays… so I’ve not a hope