AI made a high heel shoe today and when I made the heel I ran into a problem. I rolled the gumpaste and cut the heel and toe out. First I placed the toe part on the sole and once I put the heel on the edges started cracking when I tried to form the shape of the heel. I'm a newbie but I'm guessing that even though it took less than five minutes, I shouldn't have let the heel set out while placing the toe part. Is there any way to prevent this from happening?

sure--but you pretty much answered your own question

you can't let it set out--just keep it well covered because it dries out fast