How should I level the ground for my above ground pool?

In my area we get about 3.5 seasons hot enough to swim and I have a limited budget. What I have been doing is setting up an inflatable ring pool (14′ x 3.5′) to cool off in. The problem is my yard has a slope. My strategy is good I think. I place a board in the middle on a 2.5′ bolt and try to work around with a level, digging the high areas and building the low areas and adding lots of play sand. See the images for examples.

My problem is the far side (where the wall is) always compresses and the pool leans as you can see in the third image. I am constantly afraid a kid will kick against that wall after the water is high and the whole thing will just roll down the hill.

What should I do that could solve this issue for less than $100?

Sounds like the sand is shifting. Like Tester said, you may need to build up the low side with something more secure, like using those landscaping blocks with a bottom layer that is at least half in the ground. Then backfilling with dirt and compacting it.

I used yellow sand for my foundation. It’s a mix of sand and clay. I filled the whole form and located where my pool will be. Leveled the best i could( I did good). pick out the hard clumps and just put a little sand in my circumference for softness. Now I’ll put my liner down. Set up my pool. As it fills i will walk the perimeter to check for any spots i dont like before it gets to full. Then I’ll take my silica sand and surround the outer side of pool for some added support. Its just a 10×30.