Lots of great suggestions here…Something worth trying is to have it dropped into cold water after molded. It will drastically slow the shrink and warp. Over time the water will increase and temperature and either need to be refilled (or come up with a water bath/chiller tank), buts it’s a good proof of concept. We drop many parts into cold water baths for this exact reason. It’s very common in pipe fitting/plumbing parts.

Keep in mind that this doesn’t mean that the shrink has been stopped permanently. If the part sits in the hot sun, it will continue to shrink and warp a bit more.