Sharp edges on a three layer
Sharp edges on a three layer piece would indicate to me that you did not have a high enough top temperature, or did not soak there long enough.
Also If all three layers were the same size, the top may not fuse with the rest, as the dichoric acts as a separator. Instead make the dichoric layer a little smaller to allow the top layer to fuse with the bottom layer.
In working with glass you need to get it to the working temperature without breaking the glass through heating too fast. But even more importantly, you need to cool the glass to relieve the internal stresses. This is the annealing cool.
There is information on this and other sites about how to heat and cool glass. There is a good tech note on the bullseye glass site that is applicable to all glass.