I am no big time professional but I have built a few ponds, finished one earlier this week and it is filling as we speak. Like most of these guys have said, it doesn't appear very well constructed or compacted but you may have got by with a little of that if the dam had been a good bit taller then the overflow spillway. it is imperative that the dam be well above your spillway point so that when water does overflow it does not go over the newly constructed dam, it will fail every time.
There has never been a dam compacted well enough or built with good enough clay, to withstand water over-topping it, no matter how well it was built and compacted. Good Luck!
