specifying structuralBC constraints and boundary conditions on a solid cube

Hi, I'm trying to model the compression of a solid cube and compute the stress inside it. All the cube's faces are subjected to a constant pressure except for the top and the bottom. In order for matlab's pdetool to work, at least one surface should be set 'fixed' using structuralBC (otherwise it throws 'Rigid body motions not fully restrained' error). However, this leads to unwated stress near the edges. Is there a way to model an object that is in equilibrium due to equal and opposit forces without using the constraint 'fixed'.

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model=createpde();


g=multicuboid(0.2,0.1,0.05);

figure(1)
pdegplot(g,'FaceLabels','on','FaceAlpha',0.5)

smodel=createpde('structural','static-solid');

smodel.Geometry=g;
msh = generateMesh(smodel)

E=82e9;
nu=0.206;

structuralProperties(smodel, "YoungsModulus", E, "PoissonsRatio", nu)


structuralBC(smodel, 'Face', 2, 'Constraint', 'fixed')

p1 = 10e6;

structuralBoundaryLoad(smodel, 'Face', [3:6], 'Pressure', p1)
 

Rs=solve(smodel);

figure(3)
pdeplot3D(smodel, 'ColorMapData', Rs.VonMisesStress, 'Deformation', Rs.Displacement, 'DeformationScaleFactor', 100)
title('Von Mises Stress')