You need to set your community profile as well as your inventory to public (setting it just to "logged in users only" won't work!).

1. Open your steam profile and click on Edit Profile, you'll end up at this page.
2. Click on "My Privacy Settings" and select "Public - Viewable by anyone on the World-Wide Web" in both the "Profile Status" and "Inventory" sections.
   • You don't need to disclose your Steam Gift inventory, unless you want to use game banking.
3. If you have done that, click the "redo validation" link in the warning message at the top of the page.

If that does not work, try relogging from Scrap.tf. If the message is still present after that, repeat the process after some time has passed (we recommend 30 to 60 minutes) as Steam sometimes takes a while to update its status properly.