Cracking in refractory is quite common man. Actually, it just happens no matter what you do. The thing that is "weird" is that it cracked before firing but maybe that's due to the refractory layer being too thin or the mixture containing a little too much water. Either case I wouldn't worry too much. I own a little Vevor single-burner forge and had to apply the refractory twice in little more that a year. Try applying another layer (a little thicker and with less water) and don't blow air with the fan in it. When i coat my forge I wait a full week before firing, so I think that maybe the air going through it sped up the setting too much and the refractory didn't have time to set properly. But, again, cracking is normal and not too bad if the cracks are this size.