Well, I'm lucky I even got it this good. I just could not get the shape and perspective of certain things right. Notice that Rei's head is smaller than Askua's despite her being closer, for one, and that Rei's head is undersized compared to her body. Asuka's legs aren't right either, one is smaller, shorter, and thinner than the other, and they don't meet her body at quite the right level. Also, the background is slanted at an angle, as if looking from above, but then other elements of the drawing are shown as if being seen from ground level, giving instead the impression that one side of the pool is actually taller than the other side, which makes no sense considering the water level.
There's a ton of other things I think could have been done better too, but I just got so burned out with trying to figure out why the construction wasn't doing what I wanted it to that I got exhausted and had to force my way through the rest of it.