Some tips :
1- In Game options put Steering Lock to max
In car set up :
2- Add more Front and Rear Wings. It's the slowest track of the calendar so don't be shy to put them at max, then lower down Rear Wing a bit if you're not fast enough.
3- Differential : I don't remember how it works in GP4 but basically if it's hard to enter into the curve lower down the deceleration, and maybe the acceleration too to help the car to slide at the exit.
4- Spring/Bump/Rebound/ARB : soften Front and/or stiffen Rear
All of these may help