Hey! how large exactly is that image? Normally you should be able to zoom to display the whole image. As for the resizing: Yes, ditherdragen resizes the image to have 1:1 pixel sizes, but you can use any image editor like GIMP to scale up the image again to any desired resolution. to make sure pixelart is not distorted make sure to only scale up by whole integer steps, e.g. x2, x3, x4, etc…
Hope that helps :)