High LJ (SR) in graphene sheet minimization

I have tried to simulate graphene - water interaction using gromacs. I generated the itp file using the tutorial attached:

But I am obtaining a very high LJ (SR) potential on minimization and even in equilibriation (order of 1e+06). I have taken care of pbc in x and y and I have given sufficient vacuum in z to avoid interaction with the periodic images. May i please know the issue to troubleshoot?

I have verified the number of bonds to be correct based on the number of atoms also.