Hi and welcome!

You've gotten good advice. It's not just level ground you need, but you need it, it is stable level ground that won't wash away. If your newly level area is stable I would, at a minimum, put a single tarp bigger than the pool under it to prevent rocks from cutting the bottom. Intex inflatable pools are tough but the sides are much more heavily reinforced than the bottom because they are structural. You could also put a few inches of gravel followed by 2 or 3 inches of sand, but, again, it has to be stable so it doesn't wash away.

It's one of the traps of the Intex pools. You are intrigued by the low up-front cost to get a pool...but if you do not have a level surface you have make one. You've done it the easier way, going down rather than up, so it's more likely to be stable. When I had a 15' Intex donut, one of the earliest ones, I had to build a base. Even doing most of the work myself (I'm able to use a level and even a transit), it still cost me about $400 for my base and I had to "refresh" it every year to make sure it was level.

I hope this helps.

Carl