2" in 10' seems pretty steep for runoff, can you measure it? You really don't want to be more than an inch off - donut (easy set) pools will lean toward the low side (I know 'cause I've done it). I set up a similar pool on concrete at my parents house for my kids while we were visiting, I put 1/4" styrofoam under the pool to keep sand and sharp points from puncturing the pool (and to make it softer underfoot). I used the folding styrofoam that you'd put under vinyl siding. Maybe you could stack foam like that in inverted terraces to try to level the pool.