Maybe check the export or if you have any layers on your project (especially if you're using Aseprite as I have this happen time to time when merging layers or not before exporting.) You also listed 18 colors but even ignoring the multiple transparency issues here there are more than 18.
You can edit the upload by clicking the pencil icon and reuploading the art as if you were uploading it the first time if you'd like, just rename your file. You're also free to just edit color count to the correct amount, which looks closer to 53 without the weird transparency stuff lol
Regardless, looks nice, looking forward to seeing more from you and welcome to the site ^^/ ♥
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This is pretty good for a first go! Looks really nice ^^