Hmm.. seems like you want a nested policy but it become peculiar because it ends having has two class-default.
Please configure a simple priority for serial interface. It doesn't need to be shaped and nested as you can configure FR native parameters for shaping as frame-relay commands.
(that is, you only need nesting under shaping for interfaces where you have no congestion or backpressure, e.g a fastethernet where you want to send only a certain amount of traffic).
Verify results with packet generator and latency/jitter analyzer if available, then you can experiment modifications for different values, drop strategies, etc.
hope this helps, please rate post if it does!