+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.Depends. How do you feel about an indoor swimming pool?
No but seriously. That level shows more than a little off. I'd shim it up or you may have problems later. Not worth the risk.