Phishwaves,
We're at the end of our third season now, and the bow has not gotten any worse. In fact, it hasn't changed at all.
I'm certainly no pool installing expert, but it seems like 2-3 inches at the middle (would be like 4-5 inches out of plumb at the bottom?) is way too much. Maybe I'm not understanding exactly what you're saying though. Mine only leans out about an inch overall, and that's a conservative estimate. At any rate, I'll ask the same questions the other forum members asked me.
Did you put concrete pads under the ends of the buttresses and each joint?
Did you tamp the ground firmly before setting the pads?
Was the soil around the pool disturbed before you set up your pool? You didn't do any back-filling, did you?
As for the difference in water level, I would confirm with where ever you purchased the pool to see if that is a problem. (assuming it's new) Otherwise, I defer to the experts here for an answer. For me, that's too much difference, but I'm pretty particular about things like that. I used a transit to level everything from end to end, so my water level is within 1/4". Are you measuring from the coping or the pattern on the vinyl? If the liner has stretched a bit here and there, that could exaggerate your measurement.
Good luck!