Hey bud, welcome to the forum.
I don't see an attachment, but maybe I'm just being silly. In my experience, tanks (especially those bought from brands commonly held in pet stores) don't always sit completely flush. My 40B and 55 had slight problems with that before. Some people use styrofoam, but the effectiveness and what it actually does is a little debated. When I set my tanks up on the stands that I built, they weren't completely flush and upon filling, both the tank and stand flex a little bit and generally accommodate room.
That being said, if the gap is larger you might want to resurface the stand using some plywood.
Hope this helps, it's been a while since I set up a tank that wasn't completely flushed so I might be a little rusty.
“Books are my friends, my companions. They make me laugh and cry and find meaning in life.” ― Christopher Paolini, Eragon
"By books you mean fish, right?" ― Raymond