I would find the lowest point and dig the higher ground out to be level with that low point. If you fill the lowest point in with dirt, it will eventually compact and you'll be stuck again with an unlevel pool.
The foundation of the pool is the most important factor to a level pool. It takes time but it's worth it in the end! When I installed my 24' above ground, I used a 4' level and placed all my pavers <I don't think you'll use pavers> and set them level the whole way around. Then I prepared my sand bottom by hand packing it with water srayed from the hose, sand and then pulling it level after packing using the edge of the level as a trial. I leveled across and up and down in little sections. I also found out that you could walk on the packed sand as long as it was wet! It does not have to be soaking wet and I didn't hit it with a full stream of water either.
Just think, light feet. I never had a problem and I don't have a foot print on the bottom of my pool either! This is just how I did it.
I am satisfied with the hard work I put into my pool. I took my time and it paid off. I can't wait to do my inground!
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