If as you describe you were having to lift off mid corner then you were pushing the car too far plain and simple. Either you entered the corner too fast and washed out, or you entered ok and put too much throttle coming out the corner washing wide meaning you had to lift off.
To change that with aerodynamics, you would need to spend thousands and preferably have access to a decent simulator software or a wind tunnel....
however you would be able to go faster by refining your driving, eg left foot braking to reduce the front understeering rather than just lifting off.
Then if you want to spend money, suspension, bushes, sticky tyres etc wouldnt cost you much but would achieve far more grip in the real world.
we arent having a go at you, just a lot of people here have a LOT of experience with pumas handling and even modifications.
Unless youre doing it for the sake of it, you will just be wasting your time and money for little gain if you go down just the down force route.
Several pumas in the UK are run in sprint and race championships and even when they are allowed to modify aero, very few make any major mods as it just doesnt make that much difference for the level of performance most pumas will ever have.
even my car with 350bhp plus just doesnt need tons of aero. My car is biased towards RWD with the torque split, and even then, the F2 spoiler provides more downforce than i could ever need. In fact at high speed, despite the front matching splitter, above 120mph you can feel the back being pushed down heavily and above 140mph its enough to make the front go light.....
so unless you are running crazy power in a high calibre race formula then you just dont need to spend all your effort on downforce.
