jb--- I have never heard of too much rain for new seeds. You want to keep them wet all the time until they germinate.
I think the concern with heavy rain is that it can actually wash the seed away, especially on slopes and hills. Your best bet would be to try and see if the seed is still there. This may be difficult if the seed was mixed into the soil ammendments that you used (obviously, if your soil ammendment is washed away, so is the seed). My suggestion would be that if you poke around in the soil and don't see any signs of seeds, spread more....there is no such thing as too much seed!!