cracking is a part of life. There are several techniques to deal with it. Simplest thing to do is what for the carving to finish cracking, then glue wedges into the cracks and recarve.
You can also make a relief cut from the center to the outside edge to force where the crack will occur. Carvings made from half or quarter logs tend to crack much less.
I'd suggest you head over to the carving post forum and ask your question there, or use the search function to find what other people have done.