First, you'll need to drain the tank back down & loosen the bolts up some. (You do have the rubber washers on the bolts INSIDE the tank, right?)
Jiggle & pivot the tank a little to be sure it's "seated," level & square to the bowl.
Putting one forearm across the top center of the tank for some downward pressure, hand tighten the bolts. Now put your hand in the tank over one bolt & press down (firmly, but not with all your might)while tightening the nut from below. Repeat for the other side, working each bolt a little at a time. Stop when you have some visible depression in the rubber washers & the tank feels sturdy.
That's usually enough pressure to do the job. Good luck!