Just keep grinding, or take it to a machine shop and have them mill some off. DON'T press it in place! If you do that, it puts too much side load on the control arms & binds them up & also tears the sides of the poly bushings up.
Our control arms are made from wider tubing than stock, but they are fixtured up to be off to the one side slightly. This way, the measurement between the arms (where the swaybar goes) is exactly the same. You said it best when you stated that the stock swaybar fit fine. Many people report that the ATR bar is wider than the stock bar & needs grinding to fit, sometimes over 1/4".
If you get it real close, you can loosen the mounting bolts on the control arms and then fit the swaybar in place. Once you have the swaybar bolts in place, tighten the arms back up & tighten the swaybar up. Make sure you are very close before trying this, otherwiae it's just like hammering it in place.