You are replacing self.fc multiple times in these lines:
        self.fc = nn.Linear(in_features=512*7*7, out_features=4096) #25088
        self.fc = nn.Dropout(p=0.5, inplace=False)
        self.fc = nn.Linear(in_features=4096, out_features=4096)
        self.fc = nn.Dropout(p=0.5, inplace=False)
        self.fc = nn.Linear(in_features=4096, out_features=num_classes) #20

If you want to apply these layers sequentially, wrap them in an nn.Sequential container:
self.fc = nn.Sequential(nn.Linear(512*7*7, 4096),
                        nn.Dropout(),
                        ...
)