I have run a few simulations to analyse the aerodynamics of a car and get some values in terms of Cl and Cd
I am simulating 1/2 of the car thus i have used 1/2 of the total frontal area. To obtain
values for the lift and drag forces i am using the following equations L = (1/2) ρ v^2 Α CL and D = Cd * A * (1/2)* ρ * v^2 respectively.

My Cl value is 1.55 and my Cd value is 1.18
the half reference area is 0.52m^2
Velocity is 22ms^-1

To calculate the correct total lift( downforce) and drag wouldn’t i have to double my frontal area to use the total instead of the half?

After reviewing your explanation, it appears that the method you are currently using is the appropriate approach for calculating Lift and Drag coefficients when working with half geometries.

If a full model were to be used instead, it would be necessary to double the reference area. The total force (N) would also double by calculation, resulting in the same Lift and Drag coefficients being obtained.