Hi Stephanie,
What kind/brand of resin are you using?  This can be pretty typical of epoxy resins, especially certain brands.
Have you tried the Resin Obsession super clear resin?  It’s what I like to use as it maintains its shape well, even with body heat.  You can find it in several sizes in our store here:
 https://shop.resinobsession.com/collections/resin/resin-obsession
You should know that that if any epoxy is left in the sun on a metal surface, it is likely to get soft and warp.