To further my proposition that the calculations themselves may be in error:

Stuff

Now, you might be wondering how dark energy can be unknown and yet account for almost three fourths of everything. The answer lies in the very complicated math behind the basic models of cosmology. Until astronomer Edwin Hubble found that the universe was actually in motion and expanding rather than the static place scientists thought it was, there was no need to consider anything as exotic as an invisible force that pushes galaxies apart. But it was possible in Einstein’s general relativity equations which could account for an expanding or contracting universe. To make sure that all of the cosmological models in these equations stayed static, Einstein added a Λ (lambda) variable in his formulas which gave energy to theoretical empty space, the so-called cosmological constant
In the first instance, they had to re-think what they had previously been observing.

In Einstien's case, he simply added a fudge factor (he really was a genius!)

You will also see that these same theorists claim that not the world, but the universe itself is flat!