ASKING - TECHNIQUE IN EYE MOLD WITH IRIS CIRCLE

You fill the mold with resin, then pull it out and make the iris. Here, Tianba has a great video of what the process looks like after making the base.
If you want to get the dark rim like in the video, you first fill the mold with a tiny amount of color. Then add the white resin.

 

the tianba video is great, and usually what I do, or i just take a small brush and brush paint/pastel/colored uv resin around the ring, and then the part that "spills over" the edge is covered by a different color or clay or whatever else i'm using, or I'll color the iris with the clay or different color first and then paint around the ring after. theyre really nice, a bit tricky at first if you want to really take advantage, but with practice they can come out really pretty!!

 

I think I have that exact mold XD (a few because let's make lots of eyes at once!)

I bought some acrylic flatbacks to use for the pupils in mine. I think they come as small as 2mm, but 3mm and 4mm are easier to find. Got some bases painted so far, and next I'm gonna use jewellery glue (the type with a suuuper fine applicator point) to stick the flatbacks down.

It does mean you can use rhinestones and things too if you ever want to do fantasy eyes. :3

But yah, there's nothing wrong with clay. Sounds like you're doing it right!