Sometimes you have to bite the bullet and accept that you are not good enough and move on with it. A lot of people here (myself included) who didn't have issues with the event have raced the Nurburgring to death and know every corner, bump and detail of the track down to a natural level. Knowing the track properly makes an absolute massive difference in how easily you will be able to adapt to it in a crazy car like the FGT. If you have a crazy car that you're unfamiliar with, on a crazy track that you're unfamiliar with you have a recipe for pain.
As for the car, like I said, try to drive it without ever going to full throttle, you don't need full throttle to beat the AI, you can absolutely thrash them without ever (aside from the final straight) using full throttle. The problem is likely not with the setup, increasing ride height and having a more understeer balanced setup (more rear downforce, less front, softer rear suspension than the front), which will make the car easier to drive (but probably slower).
Are you using a gamepad or a wheel? Ultimately i suggest you either go practice driving the FGT on other (easier) tracks to get a better feel for its behavour, or you go practice the Nurburgring in another car (like the special event Mercedes training) to learn the track. Then go back to it in a couple of days (or weeks) and you will be fine.
Just a lasting impression. Don't try to drive the car too fast, the AI are driving fairly slowly. They can be annoying to pass on such a narrow track but they don't drive fast, you can easily beat them if you just stay on the track and drive at a decent and safe pace.