One thing I would suggest. You mention that you are building the bank up along one side to get rid of spoils. My suggestion is that unless the drainage behind that built up bank is running down hill away from the pond you want to do something so that water does not collect behind the built up bank. This can be messy depending upon where it is and you'd rather have that water in your pond. You said that things are flat with little drainage but some water from surrounding areas must flow into the pond unless you are building it on top of a hill. The pond I just built collects water from all around it via a very, very gradual slope. I did the same as you, I put the spoils on one side of the pond and made a built up area. But the important thing is that on the up hill side of the spoils I dug a very gradual sloped drainage ditch that channels the water both directions around the back side of the built up area and out each end into the pond. In the center is a high spot that allows dry access to the built up bank area while the drainage ditches going both ways channel the water into the pond. That way no water can get trapped and form little ponds along the back side of the pile. Imagine the whole thing being shaped in such a way that if the pond overlowed its banks big time the water would come up and around your built up bank area and turn it into and island with the only access being the high access spot you created which would be like a land bridge onto the island. We just got 4.5 inches of rain last week and it proved to work well. No puddles trapped behind my built up pond bank but all water flowed out the ends from behind it and into the pond thus enhancing its ability to collect water and maintain depth. I don't want to lose a single drop of what little runnoff I have.

Gotta get back to fishin!