Resin is formuated to cure in a mold w/o any air exposed to it.
When it is exposed to air, it doesn't cure properly. The wax added to the resin will surface after the resin's applied to seal the surface and exclude any air.
There're some here that can explain the chemistry that's involved, but I'm just a hobbyist.
I suspect what happened in your case is, the folks at Merton's asked you what you were doing, and when you told them repairs in your bilge, they added wax to your order.
It WON'T cure w/o it.