Seems as though your transfering too much weight forward, which will generate a lot of steering and make it feel as though you have no rear grip.
Try all or some of the following, remember that your driving style will differ from your mates etc and these changes are based on having the car at the kit standard (with ITF chassis/Top Plate).
1. Run 35wt oil #2 pistons all round with Silver rear / Gold Front springs
2. Add 1 deg Anti Dive
3. Decrease your rear droop (1mm at a time)
4. Use the Silver sway bar up front and the black on the rear
5. Lay your rear shocks over 1 hole (more inclined)
6. Level ride height will help too, say 5mm front / rear if the track is reasonably smooth
There are a lot of other things that can contribute to over steer, but for a start try the above. Most of those suggestions are about limiting the amount of weight the car transfers to the front end when you brake or get off the power.
Re-set your upper roll centres to the kit setting and make sure your running 3 deg rear toe and a neutral rear lower roll centre setting.
Ive found this car has tonnes of steering and when set up well you can push it hard and it just sticks, but I have also noticed that when I enter a corner slower than normal, I generate oversteer, so it almost beggs you to push it a little harder than expected.
As mentioned there are other things you can try but those suggestions should even out the car a fair bit, and remember to ease the throttle in mod. I found it's all about smooth accel/braking in mod.
Let us now if anything helped
Cheers
Aaron