Being new to this component I'm going to offer advice on this, but I could be wrong.

As far as I can see (I did exactly the same thing myself), there is no way to resolve this from where you are.  It seems that uploading an image creates a resized image and a thumbnail depending on your configured image size settings.  So putting the image size up in the config would not resize the images.  It may be possible to stretch the existing images, but if you did this then you would lose quality.

The only way forward I can see unfortunately would be to take your original images again and re-upload them.  I'm sorry, I know this is probably not what you want to hear, but I'm only calling it as I see it.

Hope this helps.

PS - I took all my originals and then batch uploaded them all again, this saved me a lot of time when I realized my mistake.