A quick insight from the "Lab" for you today: These are same target audience, split into age segments, the top shelf are straight CTW (to shared image post) ads, the bottom WC oCPM FB pixel (Add-To-Cart). As you can see, the CTW ads are getting more conversions at a great cost, whereas some WC ads are getting even cheaper conversions. But CTW ads are much more robust for increasing budgets. So if you want to be scaling rapidly, consider adding straight CTW ads into your mix.
Side note: If this system isn't working for your campaign, launch different campaigns! Don't be like sitting on ONE campaign to "see if this works". It's ALWAYS a numbers game. You need to launch more shirts, more campaigns, more ad sets all the time to get yourself onto the favorable side of the numbers.