This happened to me, it sounds like yours wasn't as bad as mine was. Do you have any pictures you could share?
I'll share what I did, you probably won't like it but it ended up working out really well for me in the end, although at the time I was in panic mode and had no idea what to do. Mine was a combination of the excavator being over zealous and really rocky soil that just wouldn't hold any slope.
In this
picture you can see the first dig, notice the shelf for the panels, and you can barely see the rebar in the hopper bottom that the slope should go to. I had a couple of feet of overdig here.
What I ended up doing was ordering 60 tons of roadbase and filling back in the hopper bottom, compacting and wetting every 4-6". Added some cost to the project, only took about a day of labor and a bobcat to fill it back up. Here is a
pic of it almost filled back in.
Once this was done I let it sit for a few weeks waiting for the pool panels to arrive, once those arrived I had the hopper excavated again. Here is a
pic of the second excavation, the wall slope held much better.
If you can share some pics it may help to see exactly what you are working with. Good Luck!