Mismatch about strain-stress and Young's modulus

Hi everyone!

I am doing structural analysis and I got a problem about the stress and strain. For a simple solid cube, the input Young's modulus is 2.8GPa while the obtained ratio of stress and strain is 3.2GPa. The stress is integration of tensor of the loading surface; the strain is ratio of the displacement and original length.

Is my extraction about stress and strain wrong or any missing about the model ?

Thanks in advance.