Solved by Sayed_Nadim in post #2 
              
              
                Try to change this: 
self.layer1 = nn.Sequential(
            nn.Conv2d(256, 256, 3,padding =1),
            nn.Conv2d(256, 256, 3,padding =1),
            nn.Conv2d(256, 256, 1,padding =1),
            nn.ReLU(),
            nn.MaxPool2d(kernel_size=3, stride=1, padding=1)
        )

Into this: 
se…