Project-GC doesn't have access to unpublished caches hence the "?" you see there now. As soon as your challenge cache is published (or within a reasonable time thereafter), your cache name (and country where it resides) will be shown there
To place the checker on your listing you can use the following
1. Open the link as provided
2. Click on in the "link" button on the right
3. Copy the code for the third option and paste it into your cache description
(You might need to first click on the green button above the description to put it in the right mode.)
4. Save & preview and submit for publication once you're happy with it.
If you don't see the usual challenge check icon you might need to click the Source button above the cache description box before you paste the code.