The equilibrium constant for the gas phase reaction

n2 (g) + o2 (g) 2no (g)

is k = 4.20 x 10-31 at 573 k. at equilibrium,

The equilibrium constant is found by [product]/[reactant]

If the equilibrium constant is very small, such as 4.20 * 10^-31, then that means at equilibrium there is very little product and a lot of reactant.
And likewise, if there is a lot of product formed, and very little reactant, then the K value will be very large, which tells us that it is predominantly product.

At equilibrium, for any reaction, there will always be some reactant and some product present. There cannot be zero reactant or zero product. Also keep in mind that the equilibrium constant is dependent on temperature.

At equilibrium, for your reaction, it is predominantly reactants.

Answer is to avoid experimental error