Sorry about your problems, that is a dirt borrow pit, not a pond!
esshup has given you excellent advice on your construction process, but you still need to determine if you have the right materials to complete the pond. When that is confirmed, then you can talk about the proper equipment and steps, etc.
I live in Tornado Alley, so all of the houses have basements. We do NOT like to have the foundation walls built in clay. Clay minerals will actually incorporate water into their structure, unlike sand which just allows water to exist between the particles. Therefore, when clay gets saturated it swells, and when you go through a long, dry spell it loses the water and you see the big cracks in the soil where the clay actually shrinks. That cycle is bad for foundation walls, but good for a pond because the clay usually stays saturated most of the time. (I hope your house construction concrete work makes accommodations if built on that type of material.)
Can you make clay balls when you wet your material? Even better, can you make clay pencils? If you are not sure, then you can get a clay content analysis for your material. You can even have some sand mixed in with your clay and make a tightly sealed pond. However, you must thoroughly destroy any sand layers or stringers, by cutting back and then mixing with your good material before you compact in lifts.
Is the pond mostly the size and depth that you want? If so, you could push the bad material out of the pond basin with a small or medium dozer. Then scarify the bottom (disc or break up the layers) and then perform your first compaction. You could then knock down your sides and make a 3:1 slope. If some of that material is good, then do another compacted lift to seal the bottom of the pond.
Cut the side slopes a little too deep. When you think you have the bottom sealed, then start your compaction of the sides. After the first compaction, you will need either one or two more 6" compacted lifts to finish.
Hopefully, you can rent something like a Cat CP323 or CP563. I believe those are much easier to use going up and down the side slopes than a pull behind sheepsfoot, and the vibration greatly helps the compaction.
P.S. Do you have a water source? You must wet your clay material to the proper water content to get good compaction. Do you have a buddy in the area that builds roads for government jobs? He can probably give you good pointers on how they compact the road base of local materials before they start adding the aggregate.
Good luck on turning your hole into a pond.
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