Once you have the first three locked into their open position within the seating holes, you have to bend the third quite a bit to get it to seat into the ring. I haven't used them in awhile, but I remember using my body or the floor as a point to push against. There was a video on here a while ago that explained the steps better than words can.
Just be careful not to put an eye out or rip the corners where the rods seat. The plastic covered tips obviously go toward the fabric end, the bare metal into the ring.