Not true. For example we could be surrounded by a sphere of uniform infinite density, in which case our atoms wouldn't be pulled in either direction.
Unless the sphere were infinitely far away, only the center point would be in balance, and everything else would be immediately sucked to the edge of the sphere. If the sphere's radius was infinite, that might explain the expansion of the universe itself, but not the presence of infinite density within the universe itself.
This is false. https://en.wikipedia.org/wiki/Divergence_theorem