A quick tip when resizing/editing images.
To resize/edit images the optimum process is to edit prior to importing or do so within the Content section. Resizing in the template or using the drag function can cause the image to render in an unintended size.
To resize an image, go into your campaign and double click the image. This screen should appear, to edit the height and width click the padlock to make it editable. Then readjust your width and height to your preferred size. Having the padlock closed means it will auto size the image to fit the campaign.
It may also be easier and more helpful to edit or resize images in the content library or upload images previously sized.