Just thought I'd make a comment.... just in case it is the same mistake as I made. I wonder at my own IQ sometimes.
I was trying to slip the wrong bevelled ring on - instead of the lower race, I'd been trying to slip another bevelled ring that is supposed to be situated in with the upper headset componants.
So what you describe sounds quite similar to my confusion, although I imagine a shop mechanic aint gonna be as daft as me. But who knows.
So go through all the headset parts (hopefully it's all complete) and check if there's another ring thing that is able to slip onto the lower bit of the steerer. With me, one ring was too tight, but the other was able to get seated properly.
Good luck.