Silly Blue.
They can't even can get the heights right. And you expect them to remember the jem's shape?
Silly girl.

Seriously, just look at this shit.

As it turns you see, at first, the facets match. Rose Quartz turns on its side and we see only THREE facets, matching if you took the five-faceted Rose Quartz and tipped it to the side.

After a FLASH OF WHITE LIGHT you can see they changed the number of fucking facets to match a real diamond. There's red herrings, and there's the narrative literally lying just to make the reveal work.