Thanks for translating this. Unfortunately you fell for the newbie trap and used the 1280x resolution resample pages for editing instead of the original raw which is around ~4238 x 6066. For gallery viewing, e-hentai downsamples all images to 1280x resolution so if you downloaded the pages without using the original source link, you got the reduced version instead.
Another possibility is that you downloaded the raw from one of the aggregator sites such as NH. These sites only copy galleries from e-hentai at resample quality and thus don't have the original resolution versions available. You shouldn't use these sites as a source for your raws.
Always check that you're using the original raw before you start editing. If you ever see the resolution being 1280x something, then most of the time that means something is wrong and you got the wrong version.
Here's some ways you can download the original full resolution version of any gallery on e-hentai: 1) Torrent download if a torrent is available. Avoid any torrents labeled 1280x though. 2) Click on Archive download and then Download Original Archive. 3) If you prefer to download one page at a time, make sure you download using the Download Original Source link located below each opened image in the gallery. 4) Look up the JP title on Sukebei, nearly every JP raw is on there in original quality.