+1 that's way off. If you fill the tank as it sits, you're going to be at least an inch off from your water line on the other side of the tank. Shim it up until it's perfect, front to back and side to side. Good luck :beer:
+1 You still can correct it and you should. When fishtank is not leveled, silicon seams on the side where it lean towards have to withstand greater force and therefore weaken structural integrity of the tank. Just use some plastic or cedar wood shims to level it.