The error message points to an activation, which has a too small input shape.
conv2 and conv3 are using a kernel shape of [1, 50], which would mean that the activation input shape should be at least equal.
Note that the first conv will only create an output of [batch_size, 64, 5, 1], which is too small for the second conv:
x = torch.randn(1, 1, 5, 50)
conv = nn.Conv2d(1, 1, kernel_size=(1, 50), stride=(1, 1))
out = conv(x)
print(out.shape)
> torch.Size([1, 1, 5, 1])