Hi Lori,
What happened is that the resin cured next to the wax paper. Wax paper is great in that resin doesn’t stick to it, but it does leave this mark. You can try recoating with another layer of resin, but you will most likely see the frosty surface underneath. You can try sanding the surface with a wet/dry sandpaper. Start with a 400 grit and work your way down to a 1000 grit or higher paper. You can recoat with resin then and should not be able to see the blemish.
It’s good that you want to cover your pieces during curing as dirt and dust will get into it in no time! In the future, I would suggest using plastic domes (large food containers or plastic totes work well) to cover your pieces.