More reactants must be converted to products (thus increasing Q) to achieve equilibrium (when Q = K).
To reach equilibrium, products must be converted to reactants (thus decreasing the value of Q until Q = K).
The value of Qc is less than the value of Kc (Qc < Kc), so the reaction is not at equilibrium. It must proceed to equilibrium by converting more NO2 to N2O4, thus increasing [N2O4] and decreasing [NO2] until Qc = Kc.