You seem to be confused about a number of things. First, Einstein never predicted an accelerating expansion. In various versions of his models, he predicted accelerated contraction, decelerated expansion, and a lack of either expansion or contraction. His models with no expansion or contraction included something called the cosmological constant, and models with a cosmological constant can include accelerated expansion, but Einstein himself never posited such a model (though others very shortly after him did).
Second, what we find from observation is that the Universe is in fact expanding and accelerating its expansion, and the form of its acceleration appears to match what would be expected from a cosmological constant (though the preferred term nowadays is “dark energy”, it behaves the same way). This was surprising when discovered, because most cosmologists, in the time since Einstein, had come to doubt the existence of the cosmological constant. If this state of affairs continues (and we have no reason to expect that it will not, though there is much we don’t know), then the Universe will never re-contract, nor even slow the acceleration of its expansion.