Hi Stephanie,
The challenge is going to be that when the surface of the glass gets wet, it’s not going to look as shiny. What the resin did to your sea glass is no different that what I would expect if you put your sea glass in water. Here are a couple of suggestions:
1. Take the sea glass and rough it up with some very coarse sandpaper.
2. Apply some kind of coating that makes the sea glass look frosted. I know there are aerosol sprays that add a frosted look to glass. I would try coating your glass with a frosted spray, then test it. You may need to coat it with a second, clear spray, in order for the frosted spray to stay frosted looking when it gets wet.
If you give this project a try, please let us see some pictures!