My big question would be how did it take you so long to do 2 yards of mulch? Were the beds just a total disaster?
Let me also add, as a previous poster mentioned if you tell a customer $200 + materials that will be all they hear. No customer wants you to tell them your going to be adding on a price at the end. You need to learn to be able to give a solid bid from the start and then stick with it.
That said, its a learning experience and I would bet most will say they have messed up bids when first starting. Most of the time the only way to learn is to get your hands dirty