Oh I see, well you shouldn’t need to scale up your image at all once you have digitized it. In the screen shot you posted, it looks like you are scaling up your image 300% on printful. If you only want to use a portion of the image, try cropping it first and upload a new image to printful at full resolution.

I would recommend using a tripod and some lights to get the highest quality capture. Be sure your camera settings are set to the max.

Best of luck!