Some advice if you have trouble with the formula Gran turismo, first go to brakes and set them to something like 4-1 5-2 (front-rear). Then when you drive it, dont brake like you brake with touring car, usually, with the formula, you just press slightly the brakes, downshift, then let the decelaration do most of the works and repeat. That's how I done it and I usually have 40+ sec lead after each race, except in Monaco where it was a bit harder but I just did that track in F1 2010 and it was maybe 10 times harder so yeah lol.
The trick is really to let the car decelarate and not push the brake too much.
There's some nice tunning for that car around the forum, after you should have no trouble beating that championship. Also remember it's a championship so you dont have to win all race on the first try.
I use DS3 btw but with trigger for acc/brake.