Inductance of air core coil with small diameter
Assuming your meter is OK and that you are measuring the inductor on its own, the only explanation is that you haven't used a calculator that takes account of the parasitic capacitance between turns. The net parasitic capacitance can make your meter read an incorrect value of impedance and give a false impression that the inductance is smaller.

So, your inductor is likely to be 270 nH but, due to its parasitic capacitance and using a test frequency that is above the coils self resonant frequency, you get an incorrect reading.