Rather than uploading the whole episode at once, why not do it bit by bit? I'm not saying that you should only post one panel per episode, but cut your existing file into chunks, then upload it to the dashboard little by little.
Or, when resizing your image, make sure to scale it proportionally so that even though the size is smaller, the ratio of its width and height are still the same. Depending on what programme you use, the name of the setting may differ.