This is a known issue with DDLES/QC10 Colt style lowers and CMMG BCG. The ejector does interfere with the bolt. If you look closely at the groove in the bolt where the ejector rides, you will probably see marks where the ejector was rubbing. Some folks elected to dremel a little bit of material on the back side of the ejector and the outside elbow. Others actually dremeled the bolt area. Most people had the symptom of not being able to close the upper and lower together and get the takedown pin in.
I can't tell from your description how bad the interference is. I had this problem and the only way I could get the takedown pin in was to get the pivot pin in first, then mash the upper and lower together as far as I could, and then pull the charging handle back until the bolt cleared the ejector. This let me get the takedown pin in. Once it was in, the bolt was able to cycle ok by hand, but probably never really went into full battery. I could tell that it was very close and so I dremeled the channel in the bolt where I could see the ejector was rubbing. It didn't take much, and now my gun runs great.
Others have dremeled their ejector and they were able to get their gun running fine. If the interference is minor, its easier to take a little bit off the ejector than dremeling the bolt. I could have done mine either way. Sounds like your interference may be severe so you might have to figure out why your ejector is riding so high up.