Omnipotence is more complex than that.
There are a lot of different, nuanced views on omnipotence, that I advise you go and read about in more detail, but I'll present the basic, most common answer I've heard here.
In mainstream Christian theological thought, these views on omnipotence have become more and more restrictive as more questions are asked.
The main school of thought I've seen on this is that omnipotence means one can do anything that is possible within our cosmos, unbounded by time or potency.
What does that look like?
For example, I am not omnipotent, because if I wanted to move a rock from point A to point B, I am both bounded by potency (my ability to lift the rock) and by time (I am still bound by time; I cannot move the rock instantly).
An omnipotent entity could move any rock that can possibly exist, instantaneously.
Let's put it another way: I could ask God to turn a star into ice, instantly, and God could do so.
I could not ask God to "bring me a gneurshk", because there's no such thing as a gneurshk. There is such a thing as stars, and ice, but no gneurshk.
Just like the gneurshk, the rock that God cannot lift does not, and cannot exist, because it cannot exist within our cosmos.
Cosmoi
You might respond with; "Ok, can said rock be made outside of our cosmos?" and the basic response would be no.
Just like gneurshk makes no sense in our cosmos, rock makes no sense outside of our cosmos.
The next counter would be "Can God make a cosmos in which such a rock can exist?"
The Theological Response
At this point, we threaten to tread into the murky waters of theology, but suffice it to say that the theological response would also be "No", at least in our current view of monotheistic thinking.
God is meant to be Perfect, in this system of thought; the existence of anything more than God, inside or outside of this cosmos, nullifies God. If such a rock existed, it would nullify God's Perfect Strength, thus nullifying God's Perfection, thus nullifying God.