Fank

Hello sculptors! I need help learning a bit more about the potters plastering I'm using. I am producing a large solid form from a recent silicone mould I made last week. I cast a positive from it using potters plaster 3 days ago and there is a large crack today. I think perhaps the direct sun and hot room might be the cause for the fast shrinkage. While pouring the plaster, I inserted a cobbled support in the center for mounting later (made of wood and nails. Hopefully, this isn't a contributing cause of the crack. At this point, is it safe or even possible to add fresh plaster to repair the surface of the crack? Will this piece split at some point?