I would use a belt sander to take down the high spot on the frame. I would think that you would want the tank to set evenly on all sides including the middle. If this is a glass tank, I would most certainly make sure you have the top of the base level with the tank. I would not chance it. Take the time to make it level and you won't have to shim it and it won't be in the back of your mind if it's gonna hold or not. Just remember, water weighs roughly 8 pounds a gall + the weight of the tank and it's accessories. Styrofoam is not that strong. It will compress under such weight.
125 Gal-35 Gal Wet/Dry-Tetra-Tec PF500 HOB
(3) AuquaClear 301 Powerheads-600 GPH
Automatic Tempature Controller
5-6 Inch Sand Bed-200+ lbs of LR