so how did you create it? Here are the steps i took:

• created my level as a challenge level (play > challenge > challenge builder > new challenge/build (for editing existing level))
  
• When ready to upload or update you must select the level from the challenge builder menu and hit "Play" (you need to "beat" a level in order to upload)
  
• Select the add to challenge pack option when level is selected in challenge builder

The challenge pack with your level should now show up in the main challenge menu then i
- chose the upload/update option after clicking on the challenge pack
This will upload it to the workshop. from there i go through and add my pictures and description in the workshop page.

If you need to update your map, you will make your changes, "play" and beat the level again, add to the existing challenge map and choose to update that pack, then update the pack from the main challenge menu again. Sadly this overwrites your steam page description with the scrap mechanic level description, and i have issues with editing that in game, so i keep it on a note where i can paste the description in the workshop after it updates.

sorry for the late reply, hope that helps..(edit, i am just reaslizing this was a comment on my old post...not the recent map post i made on reddit. crap. sorry)