We know about space because evolution gave us vision. We know about time because it gave us memory. But we can't exclude that there are other dimensions. What can they be?
If I say that I ate breakfast this morning in New York, I state the time (morning) and the space (New York). But the fact that I ate breakfast is also a "dimension." Perhaps, somewhere else in that dimension, I didn't eat at all, a bit further, I wasn't born and even further, the earth doesn't exist.
Already in 1881, Nietzsche reasoned about what it would be if there was no God. Then the universe was not created and must exist for always. Infinity has fascinated us from the ancient Greek Zeno to people like Kurt Gödel and Georg Cantor. But Nietzsche reasoned that, if time is infinite, what can happen will happen, again and again, an infinite number of times. He called that, the Eternal Return.
In the strange world of Quantum, we must accept that the outcome of any event is never predictable, according to Heisenberg's principle of uncertainty. If that is the case, then yes, there are as many "you" as what is possible. But the common mistake is to think of parallel universes as beans in a jar. First of all, our universe can't be considered as a "bean." It has no center nor edge. Second, if our universe is within "something" then that "something" must be in "something else" and so on, to infinity.
A parallel universe must then be considered as a dimension in which we can't travel. Imagine a road dividing in two roads, all the time. As time goes on, we follow one road, not being able to know what happens on the others. We can't know them in the same way we can't move back in time. Or even if we could, we wouldn't be aware of it because the only way we can measure time is between the past and the present moments. It requires a "displacement on the road."