The script you’ve posted is a Dataset, not to be confused with a DataLoader.
I guess, you would like to wrap your Dataset into a DataLoader, which will add the batch dimension automatically.
Could you try your code with:
loader = DataLoader(full_dataset, batch_size=10)
test_img, test_lb = next(iter(loader))
plt.imshow(test_img[0].permute(2, 1, 0))