So far your English is good enough, much better than my French.
I think when you said rough turns you meant tight turns. The GT-R is 4WD and it can have understeer, where the front tires loose grip and you go wide in the corner. There are some things you can do with suspension tuning, but if you don't want to do that then the best advice I can give you is to brake harder or brake earlier. Use the 4WD and power to pull the car out of the corner. For a 4WD car with a lot of power I like to use "slow in, fast out" approach to corner.
If you are using the Racing Line, it might be slightly off, but usually it is pretty conservative and should have you going slow enough for a corner. If you haven't been using the Racing Line, give it a try, but you shouldn't rely on it, eventually you will be faster than it and it will slow you down. See if you can get around a tight corner a few times with it on, then turn it off and do it on your own.
Let me know if you have any more questions or if you want that translated.
I should be online tomorrow around 1500 (3PM) Pacific Standard Time (I think that would be 1800 or 6PM in Quebec) and if you want to join me in my lounge just send a friend request to GTP_Im_Sorry and we can play follow-the-leader, where you follow me and match my speed to see if that helps you get through the corners better.
Basically its what NjLowrider said, only I used about 500X more words.