Since you cast this a few times, I have to ask: did you determine the shrink ratio empirically or were you able to look it up? This is a super cool project, and I'm impressed that you got it done before the wedding!
I looked around online and answers ranged from no shrinkage to 6%. For my first attempt I split the difference (3%), then measured the actual diameter with calipers. Also I tended to err on the side of making the ring too small, as it’s pretty easy to remove material from the inside of the ring.
