The Inception model expects input data with the size [batch_size, 3, 299, 299].
Could you try to increase the spatial size of your input and try it again?
Also note, that models.inception_v3 will return the aux_logits with the output in the default setting.
In case you don’t need the aux_logits, you should just return the first return value:
return self.model(x)[0]