Hi,sounds as if the flux [borax] has solidified around the gold.Hear until the flux is melting and dig the gold lump out with pliers.Quench the gold to shatter the fux,pickle it if possible.Remove as much molten flux from the crucibleas possible and then start again with clean flux.
I wouldn`t want to melt and cast the gold more than 3 times without adding fresh metal as it will build up oxide and become more likely to crack.