How do I use 'aux_operators' in 'TrotterQRTE' time evolution problem?

I'm trying to evolve a 3 qubit system under a Pauli Sum Hamiltonian in QISKIT using the TrotterQRTE method, and observe the projection of on the singlet state at every time step. How do I program the singlet projector properly in 'aux_operators'?

def TimeEvolve(theta, A=A_vedral, gamma=5.):
hamiltonian = PauliSumHamiltonian(theta,A)
qr_pair = QuantumRegister(2, name="e")
qr_mol = QuantumRegister(1, name="z")
qc_initial = QuantumCircuit(qr_pair, qr_mol)
qc_initial.x(0)
qc_initial.x(1)
qc_initial.h(1)
qc_initial.cnot(1, 0)

projector = tensor(singlet_state().proj(), qeye(2)).unit().data.toarray()

time = gamma
evolution_problem = EvolutionProblem(hamiltonian, time, qc_initial, aux_operators=projector)

product_formula = LieTrotter(reps = 2)
backend = AerSimulator(method='density_matrix')#,noise_model=noise_model)
quantum_instance = QuantumInstance(backend=backend)
expectation = AerPauliExpectation()#.convert(measurable_expression)
trotter_qrte = TrotterQRTE(product_formula = product_formula, expectation=expectation, quantum_instance=quantum_instance)
evolved_state = trotter_qrte.evolve(evolution_problem).evolved_state
return evolved_state


I usually get the error "QiskitError: 'Sum of amplitudes-squared does not equal one.'". I'm only interested in measuring the first two qubits.