ConvTranspose has an ouput_size parameter.
An example from the docs:
upsample = nn.ConvTranspose2d(16, 16, 3, stride=2, padding=1)
h = downsample(input)
>>>h.size()
torch.Size([1, 16, 6, 6])

>>> output = upsample(h, output_size=input.size())
torch.Size([1, 16, 12, 12])

So, in your case, output_size = input.size() * 2