This is really too bad.
French people won’t care much if you make mistakes, as long as you are polite. If you try to communicate and you do so with a polite tone, your effort will be welcome. But if you spend precious interactive time looking for the absolutely correct form in your head, and don’t utter a word until you’ve got it perfectly formed in your mind, French people will get impatient and move on.
You need to be quick more than correct, specially when you go to Paris: it is a fast-moving city, like New York, and no-one has time for a hesitation.
Pronunciation is really important. French is an evolving language, and book French is extremely different than spoken French. So make sure you train with audio tools, always, even when you are studying grammar or verb conjugations.
Speak up! when they get shy, many people tend to speak very softly. But if you are looking for your words AND the person can’t hear you, it might be a bit too much! So don’t yell, but be careful not too whisper either.
So, get to the essential elements of what you are trying to communicate. Use very simple words and simple constructions, stay in the present tense if tenses are a problem, smile, and never forget to be polite.
I suggest you also read my article -the best way to study French for speaking