If you are worried about it now, you'll never be comfortable with it. So fix now, before the tank gets populated.
You can get wood shims, like 6 inches wide from any home supply store (lowes, home Depot, etc) usually in the lumber section (not talking about the smaller 1" wide ones, although depending on how your stand supports your tank, the 1" wide ones maybe all you need) to slide under your tank to make it level. They cut easily with a utility knife (score it and snap). They're a couple dollars a pack, and teh pack will be WAY more than you'll ever need.
Put the tank on the tank on the stand, put the level diagonal across one corner, and shim the bottom of the tank till it's level.
I don't know what you tank/stand look like so you might have to get creative with it, but it's not that difficult.
I had to do the same thing with my home built stand for my 45 gallon tank, in an 80 year old house. I probably could have left it alone without any problems, but I knew it wasn't level and you could see it wasn't level at the water line and it bugged me, so I fixed it. Nobody else probably even noticed it.