So where on your limb was the crack? Maybe your tiller was off. From the pic of the bow on the tree (still with a long string), it looks like its pretty stiff on the last half of your limbs.
I think maybe on your next bow you should slow down a little and make sure your tiller is near perfect before doing what you did, pulling 60# (target weight) 4 inches before your target draw length. IMO, the higher you want your poundage, the more exact your tiller has to be. Being that it was your first bow, maybe you were excited and rushed things. Make one of the "tillering gizmos" to be sure you limbs bend evenly.
But of course, maybe it was all the knot's fault and your tiller was perfect.