Okay I just deleted and reuploaded it. Now this thread is just orphaned. Thanks for the advice!

You did nothing wrong, but you didn't delete the large image. To be honest, I don't know how one would do that. You might need to ask a moderator like jalonso if you want to do that.

Okay I just edited and just uploaded the small image. Did I do it right? Or do I have to delete it and reupload again?

You mean you tried to upload without the "small" image? It's perfectly acceptable to upload a small image but no "detail" image. Just upload the small image as your "small" image (which you have done already), and remove the detail image, don't upload anything there.

You do not need to have a large image because PJ has a zoom feature. Your small image can be viewed at the same size as your large one, and larger.

I tried to upload without the "detail" image and I was instructed to upload one so I shrank it and uploaded the shrunk one for "detail" image. Is there a way to fix this?

The 1x version is already the preview image though. Is the preview image you currently have somehow different from the big version, aside from the size?

It doesn't fit the "preview" image, unfortunately.

There's no need to post a "detail" image if your whole piece fits as the "preview" image. If you only upload the preview image, it'll show up as the piece. There's no need to upload a zoomed version at all, since PJ has a zoom feature.